STPM3x power on initialization in UART mode

[Alexander Shafir]

Posted on May 09, 2018 at 01:29

There is some contradiction about STPM32/33/34 POR initialization:

'After POR, to ensure a correct initialization, it is necessary to perform a reset of DSP and

communication peripherals through three SYN pulses (see Section 8.6.1 on page 67) and a single SCS pulse, as shown in the figure below. SCS pulse can be performed before or after SYN pulses, but minimum startup time before reset (as indicated in Table 5 on page 17) has to be respected.'

DocID026142 Rev 7 (37/120)

'To ensure a correct initialization of DSP, it is recommended to perform a global reset

through three SYN pulses at startup and before setting configuration bits.'

DocID026142 Rev 7 (68/120

)

But at the same time evaluation board STPM32V2 can work in UART mode and no SYN/SCS pulsed at all in this case.

Qestions:

- What is the sequence to insure the correct initialization in pure UART mode (RXD/TXD only) and is there any limitations in this case?

- Is there any hardware issues that can affect the correct initialization?

#stpm34 #stpmx #stpm32-reset #stpm3x #stpm32 #stpm33

[frenchmanflat]

Posted on July 02, 2018 at 01:40

Hi Alexander,

I found the same issue. Information on several documents is contradictory. I tied EN and SCS to 3V3 (not isolated), and left SYN open. I used a Si8621 isolator like in STPM32V2 schematic, to connect to the isolated part of the circuit and the CPU. The STPM32 doesn't work, and also doesn't drive high the TXD pin as it should be, when idle and UART selected.

Next tries are:

- add a pull-up on TXD like in the STPM32V2 schematic

- tie SYN to 3V3

Do you have any update?