General
Review and verify the
following for the custom schematic design:
- Reviewed above "Common checklist for all
sections" section of the user's guide
- Timing and switching characteristics, and any additional
information available.
- Verify the IO voltage level connected based on the
buffer type implemented for the IOs used to
configure the interface
- MCASP interface configuration and signal
connections.
- Mapping of processor pin (ball number) to the required
functionality (peripheral, signal name) on custom
board (selected pin supports muxing (multiplex) the
IO for the required function) and naming of the
signal as per the processor data-sheet pin
attributes signal name column (when using standard
peripherals).
- Matching of the polarity of the peripheral data
interface signals between the processor and the
attached device (Example Mapping of TX->RX, Dout to
Din or similar connections)
- Series resistor provision for processor clock output
signal placed near to the processor pin including
value and placement
- Connection of pulldown for clock output signal near to
the attached device input
- Optional series resistors provision for the MCASP
interface signals placed near to the source.
- Connection of parallel pulls for data interface signals
(processor or attached device inputs, that can
float)
- Connection of IO supply for IO group and attached device
IO supply (connected to the same supply source)
- Interface performance (speed, data throughput,
communication errors) and signal integrity related
concerns.
- Connection of MCASP signals when connected to multiple
attached devices.
- Clock output buffering when connected to multiple
devices
- Fail-safe operation of MCASP interface.
- Addition of required bulk and high frequency capacitors,
and value
Schematic
Review
Follow the below list for
the custom schematic design:
- MCASP
interface configuration and recommended connections
(including following the IOSET for configuring
(grouping) the signals)
- Series
resistor (22Ω) added to the clock output signal
(transmit bit clock) near to the processor clock
output pin (used for retiming) and provision for
series resistor 0Ω or 22Ω for transmit frame sync
signal near to the processor clock output pin for
control of possible signal reflections
- Provision
for series resistors added (0Ω optional) for the
interface signals (to isolate for testing or for
control of possible signal reflections)
- Pulldown
(10kΩ) provision for the MCASP clock (close to
attached device clock input pin) to hold the
attached device in low state (there are cases where
the clock is stopped or paused in a low logic state
and the pulldown option is consistent with this
logic state) for all IOs configured for MCASP
interfaces
- Supply
rails connected to the IO supply for IO group
VDDSHVx or VDDSx referenced to (powered by) MCASP
peripherals and attached devices IO supply are
sourced from the same supply and follow the ROC
- Pullup
referenced to (powered by) the processor VDDSHVx or
VDDSx for corresponding MCASP instance and
signals
- Provide
provision for external pullups for MCASP interface
(Transmit or Receive) close to attached devices. The
recommendation is to add pulls to the processor and
the attached device signals (data interface - data
in, data out) that can float (to prevent the
attached device inputs from floating until driven by
the host). Pullup values used (10kΩ or 47kΩ)
- Interface
performance (speed, data throughput, communication
errors) and signal integrity related concerns have
been analyzed (simulated) when connecting to
multiple attached devices
- Connection of MCASP signals when connected to
multiple attached devices. Follow general design
guidelines to minimize stubs
- Parallel
pull added for the processor or attached device IOs
that can float
- MCASP
interface signals are not fail-safe. The
recommendation is to apply the inputs only after the
processor supply ramps
Additional
- The
recommendation is to verify fail-safe operation when
connected to external signals. Applying an external input
signal to the processor MCASP inputs before processor supply
ramps can cause voltage feed and can affect the custom board
functions.
- Connecting Two
(x2) or more devices (common clock connection, different
data signals connection, working simultaneously) to MCASP
interface is supported. The recommendation is to follow good
or recommended layout practices when routing the bit clock
(transmit bit clock and receive bit clock). Perform
simulations using IBIS model. The x2 devices (Example: Codec
and amplifier) are recommended to be running with the same
format (TDM/I2S/etc) and Codec and amplifier are recommended
to be running with the same format (TDM/I2S/etc) and word
size setup are synchronized with the bit clock and frame
Sync.
- External ESD
protection when the interface signals are connected directly
to external inputs.