SLES248A May   2009  – March 2015 PCM1795

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
      1. 6.7.1 Digital Filter
      2. 6.7.2 Digital Filter: De-Emphasis Filter
      3. 6.7.3 Analog Dynamic Performance: Supply Voltage Characteristics
      4. 6.7.4 Analog Dynamic Performance: Temperature Characteristics
      5. 6.7.5 Analog FIR Filter performance in DSD Mode
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Audio Data Interface
        1. 7.3.1.1 Audio Serial Interface
        2. 7.3.1.2 PCM Audio Data Formats and Timing
        3. 7.3.1.3 External Digital Filter Interface and Timing
        4. 7.3.1.4 Direct Stream Digital (DSD) Format Interface and Timing
        5. 7.3.1.5 TDMCA Interface
        6. 7.3.1.6 Analog Output
    4. 7.4 Device Functional Modes
    5. 7.5 Programming
      1. 7.5.1 System Clock and Reset Functions
        1. 7.5.1.1 System Clock Input
        2. 7.5.1.2 Power-On and External Reset Functions
      2. 7.5.2 Function Descriptions
        1. 7.5.2.1 Zero Detect
      3. 7.5.3 Serial Control Interface
        1. 7.5.3.1 SPI Interface
        2. 7.5.3.2 Register Read/Write Operation
      4. 7.5.4 I2C Interface
        1. 7.5.4.1 Slave Address
        2. 7.5.4.2 Packet Protocol
        3. 7.5.4.3 Write Register
        4. 7.5.4.4 Read Register
        5. 7.5.4.5 Noise Suppression
    6. 7.6 Register Maps
      1. 7.6.1 Mode Control Registers
        1. 7.6.1.1 User-Programmable Mode Controls
        2. 7.6.1.2 Register Map
        3. 7.6.1.3 Register Definitions
          1. 7.6.1.3.1  R/W: Read/Write Mode Select
          2. 7.6.1.3.2  ATx[7:0]: Digital Attenuation Level Setting
          3. 7.6.1.3.3  R/W: Read/Write Mode Select
          4. 7.6.1.3.4  ATLD: Attenuation Load Control
          5. 7.6.1.3.5  FMT[2:0]: Audio Interface Data Format
          6. 7.6.1.3.6  DMF[1:0]: Sampling Frequency Selection for the De-Emphasis Function
          7. 7.6.1.3.7  DME: Digital De-Emphasis Control
          8. 7.6.1.3.8  MUTE: Soft Mute Control
          9. 7.6.1.3.9  R/W: Read/Write Mode Select
          10. 7.6.1.3.10 REV: Output Phase Reversal
          11. 7.6.1.3.11 ATS[1:0]: Attenuation Rate Select
          12. 7.6.1.3.12 OPE: DAC Operation Control
          13. 7.6.1.3.13 DFMS: Stereo DF Bypass Mode Select
          14. 7.6.1.3.14 FLT: Digital Filter Roll-Off Control
          15. 7.6.1.3.15 INZD: Infinite Zero Detect Mute Control
          16. 7.6.1.3.16 R/W: Read/Write Mode Select
          17. 7.6.1.3.17 SRST: System Reset Control
          18. 7.6.1.3.18 DSD: DSD Interface Mode Control
          19. 7.6.1.3.19 DFTH: Digital Filter Bypass (or Through Mode) Control
          20. 7.6.1.3.20 MONO: Monaural Mode Selection
          21. 7.6.1.3.21 CHSL: Channel Selection for Monaural Mode
          22. 7.6.1.3.22 OS[1:0]: ΔΣ Oversampling Rate Selection
          23. 7.6.1.3.23 R/W: Read/Write Mode Select
          24. 7.6.1.3.24 DZ[1:0]: DSD Zero Output Enable
          25. 7.6.1.3.25 PCMZ: PCM Zero Output Enable
          26. 7.6.1.3.26 R: Read Mode Select
          27. 7.6.1.3.27 ZFGx: Zero-Detection Flag
          28. 7.6.1.3.28 Read Mode Select
          29. 7.6.1.3.29 ID[4:0]: Device ID
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Connection Diagram in PCM Mode
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 I/V Section
          2. 8.2.1.2.2 Differential Section
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Application for External Digital Filter Interface
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Application for Interfacing With an External Digital Filter
          2. 8.2.2.2.2 Pin Assignment When Using the External Digital Filter Interface
          3. 8.2.2.2.3 Audio Format
          4. 8.2.2.2.4 System Clock (SCK) and Interface Timing
          5. 8.2.2.2.5 Functions Available in the External Digital Filter Mode
            1. 8.2.2.2.5.1 FMT[2:0]: Audio Data Format Selection
            2. 8.2.2.2.5.2 OS[1:0]: ΔΣ Modulator Oversampling Rate Selection
        3. 8.2.2.3 Application Curves
      3. 8.2.3 Application for DSD Format (DSD Mode) Interface
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
          1. 8.2.3.2.1 Features
          2. 8.2.3.2.2 Pin Assignment When Using DSD Format Interface
          3. 8.2.3.2.3 Requirements for System Clock
          4. 8.2.3.2.4 DSD Mode Configuration and Function Controls
            1. 8.2.3.2.4.1 Configuration for the DSD Interface Mode
            2. 8.2.3.2.4.2 DMF[1:0]: Analog-FIR Performance Selection
            3. 8.2.3.2.4.3 OS[1:0]: Analog-FIR Operation-Speed Selection
        3. 8.2.3.3 Application Curves
      4. 8.2.4 TDMCA Interface Format
        1. 8.2.4.1 Design Requirements
        2. 8.2.4.2 Detailed Design Procedure
          1. 8.2.4.2.1  TDMCA Mode Determination
          2. 8.2.4.2.2  TDMCA Terminals
          3. 8.2.4.2.3  Device ID Determination
          4. 8.2.4.2.4  TDMCA Frame
          5. 8.2.4.2.5  Command Field
            1. 8.2.4.2.5.1 Bit 31: Device ID Enable Flag
            2. 8.2.4.2.5.2 Bit 30: Extended Command Enable Flag
            3. 8.2.4.2.5.3 Bit 29: Daisy-Chain Selection Flag
            4. 8.2.4.2.5.4 Bits[28:24]: Device ID
            5. 8.2.4.2.5.5 Bit 23: Command Read/Write flag
            6. 8.2.4.2.5.6 Bits[22:16]: Register ID
            7. 8.2.4.2.5.7 Bits[15:8]: Command data
            8. 8.2.4.2.5.8 Bits[7:0]: Not used
          6. 8.2.4.2.6  Extended Command Field
          7. 8.2.4.2.7  Audio Fields
          8. 8.2.4.2.8  TDMCA Register Requirements
          9. 8.2.4.2.9  Register Write/Read Operation
          10. 8.2.4.2.10 TDMCA Mode Operation
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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7 Detailed Description

7.1 Overview

The PCM1795 is a 32-bit, 192 kHz, differential current output stereo DAC that comes in a 28-pin SSOP package. The PCM1795 device is software controlled through I2C or SPI, and utilizes the advanced segment DAC architecture from TI in order to perform with a Stereo Dynamic Range of 123 dB (126 dB Mono) and SNR of 123 dB (126 dB Mono) with a THD of 0.0005%. The balanced current outputs allow the user to customize the analog performance externally.

The PCM1795 device will use the SCK input as its system clock and automatically detect the sampling rate of the digital audio input and has a high tolerance for clock jitter. The PCM1795 device supports both PCM and DSD formats for audio input along with the TDMA or time-division-multiplexed command and audio-data format. The internal filter can be bypassed to allow for an external digital filter to be used.

7.2 Functional Block Diagram

PCM1795 fbd_les248.gif

7.3 Feature Description

7.3.1 Audio Data Interface

7.3.1.1 Audio Serial Interface

The audio interface port is a three-wire serial port. It includes LRCK (pin 4), BCK (pin 6), and DATA (pin 5). BCK is the serial audio bit clock, and it is used to clock the serial data present on DATA into the serial shift register of the audio interface. Serial data are clocked into the PCM1795 on the rising edge of BCK. LRCK is the serial audio left/right word clock.

The PCM1795 device requires the synchronization of LRCK and the system clock, but does not need a specific phase relation between LRCK and the system clock.

If the relationship between LRCK and the system clock changes more than ±6 BCK, internal operation is initialized within 1/fS and analog outputs are forced to the bipolar zero level until resynchronization between LRCK and the system clock is completed.

7.3.1.2 PCM Audio Data Formats and Timing

The PCM1795 device supports industry-standard audio data formats, including standard right-justified, I2S, and left-justified. The data formats are illustrated in Figure 35 to Figure 37. Data formats are selected using the format bits, FMT[2:0], in control register 18. The default data format is 32-bit I2S. All formats require binary twos complement, MSB-first audio data. Figure 34 and Table 1 show a detailed timing diagram for the serial audio interface.

PCM1795 ai_tim_audio_iface_les248.gifFigure 34. Audio Interface Timing

Table 1. Serial Audio Interface Timing Characteristics for Figure 34

MIN MAX UNIT
t(BCY) BCK pulse cycle time 70 ns
t(BCL) BCK pulse duration, low 30 ns
t(BCH) BCK pulse duration, high 30 ns
t(BL) BCK rising edge to LRCK edge 10 ns
t(LB) LRCK edge to BCK rising edge 10 ns
t(DS) DATA setup time 10 ns
t(DH) DATA hold time 10 ns
LRCK clock data 50% ± 2 bit clocks
PCM1795 ai_tim_audio_standard_les248.gifFigure 35. Audio Data Input Format: Standard Data Format (Right-Justified), Left Channel = High, Right Channel = Low
PCM1795 ai_tim_audio_left_les248.gifFigure 36. Audio Data Input Format: Left-Justified Data Format, Left Channel = High, Right Channel = Low
PCM1795 ai_tim_audio_i2s_les248.gifFigure 37. Audio Data Input Format: I2S Data Format, Left Channel = Low, Right Channel = High

7.3.1.3 External Digital Filter Interface and Timing

The PCM1795 device supports an external digital filter interface that consists of a three- or four-wire synchronous serial port that allows the use of an external digital filter. External filters include the Texas Instruments’ DF1704 and DF1706, the Pacific Microsonics PMD200, or a programmable digital signal processor.

In the external DF mode, LRCK (pin 4), BCK (pin 6) and DATA (pin 5) are defined as: WDCK, the word clock; BCK, the bit clock; and DATA, the monaural data. The external digital filter interface is selected by using the DFTH bit of control register 20, which functions to bypass the internal digital filter of the PCM1795 device .

When the DFMS bit of control register 19 is set, the PCM1795 device can process stereo data. In this case, ZEROL (pin 1) and ZEROR (pin 2) are defined as left-channel data and right-channel data input, respectively.

Detailed information for the external digital filter interface mode is provided in Application For External Digital Filter Interface.

7.3.1.4 Direct Stream Digital (DSD) Format Interface and Timing

The PCM1795 device supports the DSD format interface operation, which includes out-of-band noise filtering using an internal analog FIR filter. For DSD operation, SCK (pin 7) is redefined as BCK, DATA (pin 5) as DATAL (left channel audio data), and LRCK (pin 4) as DATAR (right channel audio data). BCK (pin 6) must be forced low in the DSD mode. The DSD format interface is activated by setting the DSD bit of control register 20.

Detailed information for the DSD mode is provided in Application For DSD Format (DSD Mode) Interface.

7.3.1.5 TDMCA Interface

The PCM1795 device supports the time-division-multiplexed command and audio (TDMCA) data format to enable control of and communication with a number of external devices over a single serial interface.

Detailed information for the TDMCA format is provided in TDMCA Interface Format.

7.3.1.6 Analog Output

Table 2 and Figure 38 show the relationship between the digital input code and analog output.

Table 2. Analog Output Current and Voltage(1)

PARAMETER 800000 (–FS) 000000 (BPZ) 7FFFFF (+FS)
IOUTN (mA) –1.5 –3.5 –5.5
IOUTP (mA) –5.5 3.5 –1.5
VOUTN (V) –1.23 –2.87 –4.51
VOUTP (V) –4.51 –2.87 –1.23
VOUT (V) –2.91 0 2.91
(1) VOUTN is the output of U1, VOUTP is the output of U2, and VOUT is the output of U3 in the measurement circuit of Figure 53.
PCM1795 ai_io-code_les248.gifFigure 38. Relationship Between Digital Input and Analog Output

7.4 Device Functional Modes

  • SPI Mode is selected by connecting MSEL to DGND. SPI mode uses four signal lines and allows higher speed full-duplex communication between the host and the PCM1795 device.
  • I2C Mode is selected by connecting MSEL to VDD. I2C uses two signal lines for half-duplex communication, and used in a variety of devices.
  • I2S input Mode is selected by default and is controlled by Register 20 bit 5.
  • DSD input Mode is selected by setting Register 20 bit 5 high.
  • TDMCA Mode is enabled when the PCM1795 device receives an LRCK signal with a pulse duration of two BCK clocks.

7.5 Programming

7.5.1 System Clock and Reset Functions

7.5.1.1 System Clock Input

The PCM1795 requires a system clock to operate the digital interpolation filters and advanced segment DAC modulators. The system clock is applied at the SCK input (pin 7). The PCM1795 has a system clock detection circuit that automatically senses the frequency at which the system clock is operating. Table 3 shows examples of system clock frequencies for common audio sampling rates. If the oversampling rate of the delta-sigma (ΔΣ) modulator is selected as 128 fS, the system clock frequency is required to be greater than 256 fS.

Figure 39 and Table 4 show the timing requirements for the system clock input. For optimal performance, it is important to use a clock source with low phase jitter and noise. The Texas Instruments PLL1700 family of multiclock generators is an excellent choice to provide the PCM1795 system clock.

Table 3. System Clock Rates for Common Audio Sampling Frequencies

SAMPLING FREQUENCY (kHz) SYSTEM CLOCK FREQUENCY (fSCK) (MHz)
128 fS 192 fS 256 fS 384 fS 512 fS 768 fS
32 4.096(1) 6.144(1) 8.192 12.288 16.384 24.576
44.1 5.6488(1) 8.4672 11.2896 16.9344 22.5792 33.8688
48 6.144(1) 9.216 12.288 18.432 24.576 36.864
96 12.288 18.432 24.576 36.864 49.152(1) 73.728(1)
192 24.576 36.864 49.152(1) 73.728(1) X(2) X(2)
(1) This system clock rate is not supported in I2C fast mode.
(2) This system clock rate is not supported for the given sampling frequency.
PCM1795 ai_tim_sysclk_les248.gifFigure 39. System Clock Input Timing

Table 4. System Clock Input Timing Characteristics for Figure 39

MIN MAX UNIT
t(SCY) System clock pulse cycle time 13 ns
t(SCKH) System clock pulse duration, high 0.4t(SCY) ns
t(SCKL) System clock pulse duration, low 0.4t(SCY) ns

7.5.1.2 Power-On and External Reset Functions

The PCM1795 includes a power-on reset function, as shown in Figure 40. With VDD > 2 V, the power-on reset function is enabled. The initialization sequence requires 1024 system clocks from the time VDD > 2 V. After the initialization period, the PCM1795 is set to its default reset state, as described in Mode Control Registers.

The PCM1795 also includes an external reset capability using the RST input (pin 14). This feature allows an external controller or master reset circuit to force the PCM1795 to initialize to the default reset state.

Figure 41 and Table 5 show the external reset operation and timing. The RST pin is set to logic 0 for a minimum of 20 ns. The RST pin is then set to a logic 1 state, thus starting the initialization sequence that requires 1024 system clock periods. The external reset is especially useful in applications where there is a delay between the PCM1795 power-up and system clock activation.

PCM1795 ai_tim_por_les248.gifFigure 40. Power-On Reset Timing
PCM1795 ai_tim_exrst_les248.gifFigure 41. External Reset Timing

Table 5. External Reset Timing Characteristics for Figure 41

MIN MAX UNIT
t(RST) Reset pulse duration, low 20 ns

7.5.2 Function Descriptions

7.5.2.1 Zero Detect

The PCM1795 has a zero-detect function. When the PCM1795 detects the zero conditions as shown in Table 6, the PCM1795 sets ZEROL (pin 1) and ZEROR (pin 2) high.

Table 6. Zero Conditions

MODE DETECTING CONDITION AND TIME
PCM DATA is continuously low for 1024 LRCKs.
External DF mode DATA is continuously low for 1024 WDCKs.
DSD DZ0 There are an equal number of 1s and 0s in every 8 bits of DSD input data for 23 ms.
DZ1 The input data are continuously 1001 0110 for 23 ms.

7.5.3 Serial Control Interface

The PCM1795 supports both SPI and I2C interfaces that set the mode control registers; see Table 10. The serial control interface is selected by MSEL (pin 3); SPI is activated when MSEL is set low, and I2C is activated when MSEL is set high.

7.5.3.1 SPI Interface

The SPI interface is a four-wire synchronous serial port that operates asynchronously to the serial audio interface and the system clock (SCK). The serial control interface is used to program and read the on-chip mode registers. The control interface includes MDO (pin 13), MDI (pin 11), MC (pin 12), and MS (pin 10). MDO is the serial data output, used to read back the values of the mode registers; MDI is the serial data input, used to program the mode registers; MC is the serial bit clock, used to shift data in and out of the control port; and MS is the mode control enable, used to enable the internal mode register access.

7.5.3.2 Register Read/Write Operation

All read/write operations for the serial control port use 16-bit data words. Figure 42 shows the control data word format. The most significant bit (MSB) is the read/write (R/W) bit. For write operations, the R/W bit must be set to '0'. For read operations, the R/W bit must be set to '1'. There are 7 bits, labeled IDX[6:0], that hold the register index (or address) for the read and write operations. The least significant 8 bits, D[7:0], contain the data to be written to, or the data that was read from, and the register specified by IDX[6:0].

Figure 43 shows the functional timing diagram for writing or reading the serial control port. MS is held at a logic 1 state until a register must be written to or read from. To start the register write or read cycle, MS is set to logic 0. Sixteen clocks are then provided on MC, corresponding to the 16 bits of the control data word on MDI and readback data on MDO. After the eighth clock cycle has completed, the data from the indexed-mode control register appears on MDO during the read operation. After the 16th clock cycle has completed, the data are latched into the indexed-mode control register during the write operation. To write or read subsequent data, MS must be set to '1' once.

PCM1795 ai_mdi_ctrl_word_les248.gifFigure 42. Control Data Word Format for MDI
PCM1795 ai_tim_serial_ctrl_les248.gif
NOTE: Bit 15 is used for selection of write or read. Setting R/W = 0 indicates a write, while R/W = 1 indicates a read. Bits 14–8 are used for the register address. Bits 7–0 are used for register data.
Figure 43. Serial Control Format
PCM1795 ai_tim_ctrl_iface_les248.gifFigure 44. Control Interface Timing

Table 7. Control Interface Timing Characteristics for Figure 44

MIN MAX UNIT
t(MCY) MC pulse cycle time 100 ns
t(MCL) MC low-level time 40 ns
t(MCH) MC high-level time 40 ns
t(MHH) MS high-level time 80 ns
t(MSS) MS falling edge to MC rising edge 15 ns
t(MSH) MS hold time(1) 15 ns
t(MDH) MDI hold time 15 ns
t(MDS) MDI setup time 15 ns
t(MOS) MC falling edge to MDO stable 30 ns
(1) MC rising edge for LSB to MS rising edge.

7.5.4 I2C Interface

The PCM1795 supports the I2C serial bus and the data transmission protocol for standard and fast mode as a slave device. This protocol is explained in the I2C specification 2.0.

In I2C mode, the control terminals are changed as described in Table 8.

Table 8. Control Terminals

TERMINAL NAME TDMCA NAME PROPERTY DESCRIPTION
MS ADR0 Input I2C address 0
MDI ADR1 Input I2C address 1
MC SCL Input I2C clock
MDO SDA Input/output I2C data

7.5.4.1 Slave Address

The PCM1795 has 7 bits for its own slave address, as shown in Figure 45. The first 5 bits (MSBs) of the slave address are factory preset to 10011. The next 2 bits of the address byte are the device select bits that can be user-defined by the ADR1 and ADR0 terminals. A maximum of four PCM1795 devicess can be connected on the same bus at one time. Each PCM1795 responds when it receives its own slave address.

PCM1795 ai_slave_addy_les248.gifFigure 45. Slave Address

7.5.4.2 Packet Protocol

A master device must control packet protocol that consists of a start condition, slave address, read/write bit, data if write or acknowledge if read, and stop condition. The PCM1795 supports only slave receivers and slave transmitters.

PCM1795 ai_tim_i2c_frame_les248.gifFigure 46. Basic I2C Framework

7.5.4.3 Write Register

A master can write to any PCM1795 registers using single or multiple accesses. The master sends a PCM1795 slave address with a write bit, a register address, and the data. If multiple access is required, the address is that of the starting register, followed by the data to be transferred. When the data are received properly, the index register is incremented by '1' automatically. When the index register reaches 0x7F, the next value is 0x00. When undefined registers are accessed, the PCM1795 does not send an acknowledgment. Figure 47 shows a diagram of the write operation.

PCM1795 ai_wr_op_les248.gifFigure 47. Write Operation

7.5.4.4 Read Register

A master can read the PCM1795 register. The value of the register address is stored in an indirect index register in advance. The master sends a PCM1795 slave address with a read bit after storing the register address. Then the PCM1795 transfers the data that the index register points to. When the data are transferred during a multiple access, the index register is incremented by '1' automatically. (When first going into read mode immediately following a write, the index register is not incremented. The master can read the register that was previously written.) When the index register reaches 0x7F, the next value is 0x00. The PCM1795 outputs some data when the index register is 0x10 to 0x1F, even if it is not defined in Table 10. Figure 48 shows a diagram of the read operation.

PCM1795 ai_rd_op_les248.gifFigure 48. Read Operation

7.5.4.5 Noise Suppression

The PCM1795 incorporates noise suppression using the system clock (SCK). However, there must be no more than two noise spikes in 600 ns. The noise suppression works for SCK frequencies between 8 MHz and 40 MHz in fast mode. However, it works incorrectly under the following conditions:

Case 1:

  1. t(SCK) > 120 ns (t(SCK): period of SCK)
  2. t(HI) + t(D–HD) < t(SCK) × 5
  3. Spike noise exists on the first half of the SCL high pulse.
  4. Spike noise exists on the SDA high pulse just before SDA goes low.

PCM1795 ai_tim_noise_case1_les248.gifFigure 49. Case 1

When these conditions occur at the same time, the data are recognized as low.

Case 2:

  1. t(SCK) > 120 ns
  2. t(S–HD) or t(RS–HD) < t(SCK) × 5
  3. Spike noise exists on both SCL and SDA during the hold time.

PCM1795 ai_tim_noise_case2_les248.gifFigure 50. Case 2

When these conditions occur at the same time, the PCM1795 fails to detect a start condition.

Case 3:

  1. t(SCK) < 50 ns
  2. t(SP) > t(SCK)
  3. Spike noise exists on SCL just after SCL goes low.
  4. Spike noise exists on SDA just before SCL goes low.

PCM1795 ai_tim_noise_case3_les248.gifFigure 51. Case 3

When these conditions occur at the same time, the PCM1795 erroneously detects a start or stop condition.

7.6 Register Maps

7.6.1 Mode Control Registers

7.6.1.1 User-Programmable Mode Controls

The PCM1795 device includes a number of user-programmable functions that are accessed via mode control registers. The registers are programmed using the serial control interface, as previously discussed in SPI Interface and I2C Interface. Table 9 lists the available mode-control functions, along with the default reset conditions and associated register index.

Table 9. User-Programmable Function Controls

FUNCTION DEFAULT REGISTER BIT PCM DSD DF BYPASS
Digital attenuation control 0 dB Register 16 ATL[7:0] (for left channel) Yes No No
0 dB to –120 dB and mute, 0.5-dB step Register 17 ATR[7:0] (for right channel)
Attenuation load control Attenuation disabled Register 18 ATLD Yes No No
Disabled, enabled
Input audio data format selection 24-bit I2S format Register 18 FMT[2:0] Yes No Yes
16-, 20-, 32-bit standard (right-justified) format
24-bit MSB-first left-justified format
16-/32-bit I2S format
Sampling rate selection for de-emphasis De-emphasis disabled Register 18 DMF[1:0] Yes Yes(1) No
Disabled, 44.1 kHz, 48 kHz, 32 kHz
De-emphasis control De-emphasis disabled Register 18 DME Yes No No
Disabled, enabled
Soft mute control Mute disabled Register 18 MUTE Yes No No
Soft mute disabled, enabled
Output phase reversal Normal Register 19 REV Yes Yes Yes
Normal, reverse
Attenuation speed selection ×1 fS Register 19 ATS[1:0] Yes No No
×1fS, ×(1/2)fS, ×(1/4)fS, ×(1/8)fS
DAC operation control DAC operation enabled Register 19 OPE Yes Yes Yes
Enabled, disabled
Stereo DF bypass mode select Monaural Register 19 DFMS Yes No Yes
Monaural, stereo
Digital filter roll-off selection Sharp roll-off Register 19 FLT Yes No No
Sharp roll-off, slow roll-off
Infinite zero mute control Disabled Register 19 INZD Yes No Yes
Disabled, enabled
System reset control Normal operation Register 20 SRST Yes Yes Yes
Reset operation, normal operation
DSD interface mode control Disabled Register 20 DSD Yes Yes No
DSD enabled, disabled
Digital-filter bypass control DF enabled Register 20 DFTH Yes No Yes
DF enabled, DF bypass
Monaural mode selection Stereo Register 20 MONO Yes Yes Yes
Stereo, monaural
Channel selection for monaural mode data Left channel Register 20 CHSL Yes Yes Yes
Left channel, Right channel
ΔΣ oversampling rate selection ×64 fS Register 20 OS[1:0] Yes Yes(2) Yes
×64 fS, ×128 fS, ×32 fS
PCM zero output enable Enabled Register 21 PCMZ Yes No Yes
DSD zero output enable Disabled Register 21 DZ[1:0] Yes Yes No
FUNCTION AVAILABLE ONLY FOR READ
Zero detection flag Not zero = 0 Register 22 ZFGL (for left channel) Yes Yes Yes
Not zero, zero detected Zero detected = 1 ZFGR (for right channel)
Device ID (at TDMCA) Register 23 ID[4:0] Yes No No
(1) When in DSD mode, DMF[1:0] is defined as DSD filter (analog FIR) performance selection.
(2) When in DSD mode, OS[1:0] is defined as DSD filter (analog FIR) operating rate selection.

7.6.1.2 Register Map

The mode control register map is shown in Table 10. Registers 16 to 21 include an R/W bit that determines whether a register read (R/W = 1) or write (R/W = 0) operation is performed. Registers 22 and 23 are read-only.

Table 10. Mode Control Register Map

REGISTER B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Register 16 R/W 0 0 1 0 0 0 0 ATL7 ATL6 ATL5 ATL4 ATL3 ATL2 ATL1 ATL0
Register 17 R/W 0 0 1 0 0 0 1 ATR7 ATR6 ATR5 ATR4 ATR3 ATR2 ATR1 ATR0
Register 18 R/W 0 0 1 0 0 1 0 ATLD FMT2 FMT1 FMT0 DMF1 DMF0 DME MUTE
Register 19 R/W 0 0 1 0 0 1 1 REV ATS1 ATS0 OPE RSV DFMS FLT INZD
Register 20 R/W 0 0 1 0 1 0 0 RSV SRST DSD DFTH MONO CHSL OS1 OS0
Register 21 R/W 0 0 1 0 1 0 1 RSV RSV RSV RSV RSV DZ1 DZ0 PCMZ
Register 22 R 0 0 1 0 1 1 0 RSV RSV RSV RSV RSV RSV ZFGR ZFGL
Register 23 R 0 0 1 0 1 1 1 RSV RSV RSV ID4 ID3 ID2 ID1 ID0

7.6.1.3 Register Definitions

PCM1795 ai_reg_def_16-17_les248.gif

7.6.1.3.1 R/W: Read/Write Mode Select

When R/W = 0, a write operation is performed.

When R/W = 1, a read operation is performed.

Default value: 0

7.6.1.3.2 ATx[7:0]: Digital Attenuation Level Setting

These bits are available for read and write.

Default value: 1111 1111b

Each DAC output has a digital attenuator associated with it. The attenuator can be set from 0 dB to –120 dB, in 0.5-dB steps. Alternatively, the attenuator can be set to infinite attenuation (or mute). The attenuation data for each channel can be set individually. However, the data load control (the ATLD bit of control register 18) is common to both attenuators. ATLD must be set to '1' in order to change an attenuator setting. The attenuation level can be set using Equation 1.

Equation 1. Attenuation level (dB) = 0.5 dB × (ATx[7:0]DEC – 255)

where

    For ATx[7:0]DEC = 0 through 14, the attenuator is set to infinite attenuation. Table 11 lists the attenuation levels for various settings.

    Table 11. Attenuation Levels

    ATx[7:0] DECIMAL VALUE ATTENUATION LEVEL SETTING
    1111 1111b 255 0 dB, no attenuation (default)
    1111 1110b 254 –0.5 dB
    1111 1101b 253 –1.0 dB
    0001 0000b 16 –119.5 dB
    0000 1111b 15 –120.0 dB
    0000 1110b 14 Mute
    0000 0000b 0 Mute
    PCM1795 ai_reg_def_18_les248.gif

    7.6.1.3.3 R/W: Read/Write Mode Select

    When R/W = 0, a write operation is performed.

    When R/W = 1, a read operation is performed.

    Default value: 0

    7.6.1.3.4 ATLD: Attenuation Load Control

    This bit is available for read and write.

    Default value: 0

    Table 12. ATLD

    ATLD ATTENUATION CONTROL SETTING
    ATLD = 0 Attenuation control disabled (default)
    ATLD = 1 Attenuation control enabled

    The ATLD bit is used to enable loading of the attenuation data contained in registers 16 and 17. When ATLD = 0, the attenuation settings remain at the previously programmed levels, ignoring new data loaded from registers 16 and 17. When ATLD = 1, attenuation data written to registers 16 and 17 is loaded normally.

    7.6.1.3.5 FMT[2:0]: Audio Interface Data Format

    These bits are available for read and write.

    Default value: 101

    Table 13. FMT[2:0]

    FMT[2:0] AUDIO DATA FORMAT SELECTION
    000 16-bit standard format, right-justified data, BCK ≥ x32 fS
    001 32-bit standard format, right-justified data, BCK ≥ x64 fS
    010 24-bit standard format, right-justified data, BCK ≥ x48 fS
    011 24-bit MSB-first, left-justified format data, BCK ≥ x48 fS
    100 32-bit I2S format data, BCK ≥ x64 fS
    101 24-bit I2S format data (default), BCK ≥ x48 fS
    110 Reserved
    111 Reserved

    The FMT[2:0] bits are used to select the data format for the serial audio interface.

    For the external digital filter interface mode (DFTH mode), this register is operated as shown in Application for External Digital Filter Interface.

    7.6.1.3.6 DMF[1:0]: Sampling Frequency Selection for the De-Emphasis Function

    These bits are available for read and write.

    Default value: 00

    Table 14. DMF[1:0]

    DMF[1:0] DE-EMPHASIS SAMPLING FREQUENCY SELECTION
    00 Disabled (default)
    01 48 kHz
    10 44.1 kHz
    11 32 kHz

    The DMF[1:0] bits are used to select the sampling frequency used by the digital de-emphasis function when it is enabled by setting the DME bit. The de-emphasis curves are shown in Typical Characteristics.

    For the DSD mode, analog FIR filter performance can be selected using this register. A register map and filter response plots are shown in Application For DSD Format (DSD Mode) Interface.

    7.6.1.3.7 DME: Digital De-Emphasis Control

    This bit is available for read and write.

    Default value: 0

    Table 15. DME

    DME DE-EMPHASIS SETTING
    DME = 0 De-emphasis disabled (default)
    DME = 1 De-emphasis enabled

    The DME bit is used to enable or disable the de-emphasis function for both channels.

    7.6.1.3.8 MUTE: Soft Mute Control

    This bit is available for read and write.

    Default value: 0

    Table 16. MUTE

    MUTE SOFT MUTE SETTING
    MUTE = 0 Soft mute disabled (default)
    MUTE = 1 Soft mute enabled

    The MUTE bit is used to enable or disable the soft mute function for both channels.

    Soft mute is operated as a 256-step attenuator. The speed for each step to –∞ dB (mute) is determined by the attenuation rate selected in the ATS register.

    PCM1795 ai_reg_def_19_les248.gif

    7.6.1.3.9 R/W: Read/Write Mode Select

    When R/W = 0, a write operation is performed.

    When R/W = 1, a read operation is performed.

    Default value: 0

    7.6.1.3.10 REV: Output Phase Reversal

    This bit is available for read and write.

    Default value: 0

    Table 17. REV

    REV OUTPUT SETTING
    REV = 0 Normal output (default)
    REV = 1 Inverted output

    The REV bit is used to invert the output phase for both channels.

    7.6.1.3.11 ATS[1:0]: Attenuation Rate Select

    These bits are available for read and write.

    Default value: 00

    Table 18. ATS[1:0]

    ATS[1:0] ATTENUATION RATE SELECTION
    00 Every LRCK (default)
    01 LRCK/2
    10 LRCK/4
    11 LRCK/8

    The ATS[1:0] bits are used to select the rate at which the attenuator is decremented/incremented during level transitions.

    7.6.1.3.12 OPE: DAC Operation Control

    This bit is available for read and write.

    Default value: 0

    Table 19. OPE

    OPE DAC OPERATION CONTROL
    OPE = 0 DAC operation enabled (default)
    OPE = 1 DAC operation disabled

    The OPE bit is used to enable or disable the analog output for both channels. Disabling the analog outputs forces them to the bipolar zero level (BPZ) even if audio data are present on the input.

    7.6.1.3.13 DFMS: Stereo DF Bypass Mode Select

    This bit is available for read and write.

    Default value: 0

    Table 20. DFMS

    DFMS MODE SELECTION
    DFMS = 0 Monaural (default)
    DFMS = 1 Stereo input enabled

    The DFMS bit is used to enable stereo operation in DF bypass mode. In the DF bypass mode, when DFMS is set to '0', the pin for the input data are DATA (pin 5) only; therefore, the PCM1795 operates as a monaural DAC. When DFMS is set to '1', the PCM1795 can operate as a stereo DAC with inputs of the left channel and right channel data on ZEROL (pin 1) and ZEROR (pin 2), respectively.

    7.6.1.3.14 FLT: Digital Filter Roll-Off Control

    This bit is available for read and write.

    Default value: 0

    Table 21. FLT

    FLT ROLL-OFF CONTROL
    FLT = 0 Sharp roll-off (default)
    FLT = 1 Slow roll-off

    The FLT bit is used to select the digital filter roll-off characteristic. The filter responses for these selections are shown in Typical Characteristics.

    7.6.1.3.15 INZD: Infinite Zero Detect Mute Control

    This bit is available for read and write.

    Default value: 0

    Table 22. INZD

    INZD INFINITE ZERO DETECT MUTE SETTING
    INZD = 0 Infinite zero detect mute disabled (default)
    INZD = 1 Infinite zero detect mute enabled

    The INZD bit is used to enable or disable the zero detect mute function. Setting INZD to '1' forces muted analog outputs to hold a bipolar zero level when the PCM1795 detects a zero condition in both channels. The infinite zero detect mute function is not available in the DSD mode.

    PCM1795 ai_reg_def_20_les248.gif

    7.6.1.3.16 R/W: Read/Write Mode Select

    When R/W = 0, a write operation is performed.

    When R/W = 1, a read operation is performed.

    Default value: 0

    7.6.1.3.17 SRST: System Reset Control

    This bit is available for write only.

    Default value: 0

    Table 23. SRST

    SRST SYSTEM RESET CONTROL
    SRST = 0 Normal operation (default)
    SRST = 1 System reset operation (generate one reset pulse)

    The SRST bit is used to reset the PCM1795 to the initial system condition.

    7.6.1.3.18 DSD: DSD Interface Mode Control

    This bit is available for read and write.

    Default value: 0

    Table 24. DSD

    DSD DSD INTERFACE MODE CONTROL
    DSD = 0 DSD interface mode disabled (default)
    DSD = 1 DSD interface mode enabled

    The DSD bit is used to enable or disable the DSD interface mode.

    7.6.1.3.19 DFTH: Digital Filter Bypass (or Through Mode) Control

    This bit is available for read and write.

    Default value: 0

    Table 25. DFTH

    DFTH DIGITAL FILTER CONTROL
    DFTH = 0 Digital filter enabled (default)
    DFTH = 1 Digital filter bypassed for external digital filter

    The DFTH bit is used to enable or disable the external digital filter interface mode.

    7.6.1.3.20 MONO: Monaural Mode Selection

    This bit is available for read and write.

    Default value: 0

    Table 26. MONO

    MONO MODE SELECTION
    MONO = 0 Stereo mode (default)
    MONO = 1 Monaural mode

    The MONO function is used to change operation mode from the normal stereo mode to the monaural mode. When the monaural mode is selected, both DACs operate in a balanced mode for one channel of audio input data. Channel selection is available for left-channel or right-channel data, determined by the CHSL bit.

    7.6.1.3.21 CHSL: Channel Selection for Monaural Mode

    This bit is available for read and write.

    Default value: 0

    Table 27. CHSL

    CHSL CHANNEL SELECTION
    CHSL = 0 Left channel selected (default)
    CHSL = 1 Right channel selected

    This bit is available when MONO = 1.

    The CHSL bit selects left-channel or right-channel data to be used in monaural mode.

    7.6.1.3.22 OS[1:0]: ΔΣ Oversampling Rate Selection

    These bits are available for read and write.

    Default value: 00

    Table 28. OS[1:0]

    OS[1:0] OPERATING SPEED SELECTION
    00 64 times fS (default)
    01 32 times fS
    10 128 times fS
    11 Reserved

    The OS bits are used to change the oversampling rate of ΔΣ modulation. Use of this function enables the designer to stabilize the conditions at the post low-pass filter for different sampling rates. As an application example, programming to set 128 times in 44.1-kHz operation, 64 times in 96-kHz operation, or 32 times in 192-kHz operation allows the use of only a single type (cut-off frequency) of post low-pass filter. The 128-fS oversampling rate is not available at sampling rates above 100 kHz. If the 128-fS oversampling rate is selected, a system clock of more than 256 fS is required.

    In DSD mode, these bits are used to select the speed of the bit clock for DSD data coming into the analog FIR filter.

    PCM1795 ai_reg_def_21_les248.gif

    7.6.1.3.23 R/W: Read/Write Mode Select

    When R/W = 0, a write operation is performed.

    When R/W = 1, a read operation is performed.

    Default value: 0

    7.6.1.3.24 DZ[1:0]: DSD Zero Output Enable

    These bits are available for read and write.

    Default value: 00

    Table 29. DZ[1:0]

    DZ[1:0] ZERO OUTPUT ENABLE
    00 Disabled (default)
    01 Even pattern detect 1 × 96h pattern detect

    The DZ bits are used to enable or disable the output zero flags and to select the zero pattern in DSD mode.

    7.6.1.3.25 PCMZ: PCM Zero Output Enable

    These bits are available for read and write.

    Default value: 1

    Table 30. PCMZ

    PCMZ PCM ZERO OUTPUT SETTING
    PCMZ = 0 PCM zero output disabled
    PCMZ = 1 PCM zero output enabled (default)

    The PCMZ bit is used to enable or disable the output zero flags in PCM mode and the external DF mode.

    PCM1795 ai_reg_def_22_les248.gif

    7.6.1.3.26 R: Read Mode Select

    Value is always '1', specifying the readback mode.

    7.6.1.3.27 ZFGx: Zero-Detection Flag

    Where x = L or R, corresponding to the DAC output channel. These bits are available only for readback.

    Default value: 00

    Table 31. ZFGx

    ZFGx ZERO DETECTION
    ZFGx = 0 Not zero
    ZFGx = 1 Zero detected

    These bits show zero conditions. The status is the same as that of the zero flags at ZEROL (pin 1) and ZEROR (pin 2). See Zero Detect.

    PCM1795 ai_reg_def_23_les248.gif

    7.6.1.3.28 Read Mode Select

    Value is always '1', specifying the readback mode.

    7.6.1.3.29 ID[4:0]: Device ID

    The ID[4:0] bits hold a device ID in the TDMCA mode.