SPRUJF2A March 2026 – March 2026 AM13E23019
The ULPCLK is the bus clock for peripherals in the PD0 power domain. It supports operation up to 50 MHz and is derived directly from the MCLK tree through a clock divider (MCLK/4) which is enabled only when MCLK is sourced from a high-speed clock (SYSPLL, XTAL, or HFCLK_IN). The ULPCLK frequency is dependent on the MCLK dividers configuration and the selected power mode.
The PD0 power domain has a frequency limit of 50MHz in RUN and SLEEP modes. This frequency is derived from the MCLK/4 clock tree. As such, ULPCLK must be maintained to be ≤50MHz at all times. When MCLK is configured to run from SYSOSC, SYSCTL disables the MCLK/4 divider automatically and ULPCLK is sourced from MCLK as these clock sources are always ≤32 MHz.
However, when MCLK is configured to run from a high-speed clock (SYSPLL, XTAL, or HFCLK_IN), hardware shall switch back to MCLK/4 divider. The right configuration of this divider value is the responsibility of the application software to ensure that ULPCLK is ≤50 MHz in RUN and SLEEP modes by configuring it appropriately.
MCLK/4 divider for the MCLK/4 domain is by default at /4. When MCLK < 100MHz and > 50MHz, then it can be configured to /2. When MCLK ≤ 50MHz, then it can be configured to /1. Application software shall ensure MCLK/2 and MCLK/4 dividers are configured appropriately using the MCLKDIVCFG field in the MCLKCFG register.
In STOP mode, the MCLK tree (and by extension, the ULPCLK) run from SYSOSC with a 4MHz rate. In STANDBY mode, the ULPCLK runs from LFCLK to conserve power. In SHUTDOWN mode, the ULPCLK is turned off.
| Selected Power Mode | Configuration | Register Settings | ULPCLK Frequency |
|---|---|---|---|
|
(200MHz maximum) |
MCLK source is SYSOSC | MCLKCFG.USEHSCLK=0x0 | ULPCLK is sourced from MCLK according to the MCLK configuration with fULPCLK = fMCLK |
| MCLK source is HSCLK (SYSPLL or HFCLK) | MCLKCFG.USEHSCLK=0x1 | ULPCLK is sourced from MCLK according to the MCLK configuration with fULPCLK = fMCLK/Quarter Divider | |
|
(4MHz maximum) |
STOP with SYSOSC enabled | - | ULPCLK is sourced from SYSOSC with fULPCLK = 4MHz |
|
(32kHz maximum) |
STANDBY with ULPCLK and LFCLK enabled | MCLKCFG.STOPCLKSTBY=0x0 | ULPCLK is sourced from LFCLK with fULPCLK = fLFCLK = 32kHz |
|
(Off) |
- | - | ULPCLK is off |