1. Introduction
The ST67W611M1 features a shutdown mode with a typical current consumption of 200 nA. This mode is entered by forcing the CHIP_EN module low which maintains the module in reset.
2. CHIP_EN hardware implementation
CHIP_EN is a 3.3 V signal that needs to be provided by the Host which controls the ST67W611M1. A direct connection from the CHIP_EN module pin (number 17) to a host pin is therefore mandatory. A 100 nF capacitor must be added between CHIP_EN and the ground.
A delay of at least 3.3 ms must be guaranteed between the module power-up and CHIP_EN going high.
CHIP_EN is one of the two bootstrap pins that control the boot mode of the ST67W611M1. See the BOOT related page for more details.
3. CHIP_EN state control
The host controls the ST67W611M1's CHIP_EN by forcing it low or high. In the short time until the host boots and takes control of CHIP_EN, this pin will be floating and the ST67W611M1 will be in an unknown state (see figure below).
It has been confirmed that this short time during which CHIP_EN is floating doesn't affect the module functionality. It can still be avoided by making sure CHIP_EN is forced low from board startup through an onboard pull-down. Another option is to connect CHIP_EN to a Host pin that has a known default level before the host firmware starts running.
3.1. STM32U5 example
As an example in the case of the STM32U5, JTAG and SWD pins have known default levels thanks to internal 40 kΩ pull-up or pull-down. These pins are listed below. More details are detailed in the STM32U5 reference manual.
- PA15: JTDI in pull-up
- PA14: JTCK/SWCLK in pull-down
- PA13: JTMS/SWDIO in pull-up
- PB4: NJTRST in pull-up
This kind of changes has been tested. The figure below shows the case with CHIP_EN connected on the STM32U5 PA14 pin which features a pull-down. As can be seen, CHIP_EN is no longer floating and is kept low until the firmware forces it high.
It must be noted that:
- Using a JTAG pin to control CHIP_EN means that JTAG is no longer available for the STM32U5 programming/debug.
- Using a SWD pin to control CHIP_EN means that SWD and JTAG are no longer available for the STM32U5 programming/debug. Debug would then be fully disabled, and subsequent programming would have to be done via bootloader.
4. X-CUBE-ST67W61 software system behavior
Starting X-CUBE-ST67W61 1.0.0 release, shutdown feature is supported. The module is shut down after calling CLI command "quit". See the software related documentation for more details.