Whether SYN, SCS pin connection is required when using STPM32 UART

[ckim.2390]

hello

I am studying by purchasing the EVALSTPM32 Board and connecting it to a PC via USB to Serial.

If you look at the datasheet of STPM32, you can use the SYN and SCS pins to request a reset operation when booting the chip.

However, the EVALSTPM32 board cannot control SYN when looking at the USB to Serial connection.

In addition, DSP_CR3 SW_RESET also exists in the STPM32 chip.

Question 1. What is the difference between reset using SYN and SCS and SW_RESET during chip booting?

Question 2. When using UART communication of STPM32, is there any problem if SYN and SCS are connected to VCC?

thank you.

[Marilena Gaetana SAMBATARO]

Good morning and thank you for your interest.

Concerning your questions:

1. By SYN and SCS a complete device hard reset is performed. Writing SW Reset configuration bit in DSP_CR3 brings the configuration registers to their default values, while data registers are not reset.
2. We recommend to always connect SYN and SCS to allow the correct power on reset sequence, as explained in the datasheet.

Best regards

Marilena

[ckim.2390]

Thank you for answer.

If you don't mind, can I ask you more questions?

-question-

In the product board under development, the supply power (VCC PIN, EN PIN) of the STPM32 chip can be controlled through the MCU.

And it accumulates and saves energy measurement values in MCU applications.(It does not matter if the STPM32 data register is initialized.)

Question 1

When booting with STPM32 chip's VCC power supply (OFF->ON), is it the same reset sequence process (configuration register, data register reset) even if the initialization process of SYN and SCS is omitted?

Question 2

In the situation of question 1, if you directly control the power supply of the chip, is there any problem if you connect the MCU and STPM32 to UART RX and TX only?

[Marilena Gaetana SAMBATARO · Accepted solution]

Hello,

the startup by Vcc or EN is equivalent. In both cases, SCS and SYN sequence is highly recommended to ensure proper DSP startup in every conditions (HF noise, harsh environment,.. ).

I suggest you to check AN2066 that in par. 1.2.3. suggests an alternative to connect only 3 pins instead of 4, to drive all the signals and provide the correct startup sequence.