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Voltage drop in multiple-slave SPI communication

DKari.1
Associate II

‎2021-01-12 03:40 AM

Hi,

I have two stm32f103 uc (as the slaves) which communicate with a stm32f407 (as the master) through SPI. I realized when SPI in both slaves are enabled the voltage on MISO pin drops to 2.5 Volt while when only the SPI in one of the slaves are enabled the voltage is 3.3V.

Is there any explanation for that?

It is problematic for me because in my project I have actually 6 slaves communicating to the master and when all of them are enabled the voltage drops down below 500 microvolts and the master does not understand the communication at all.

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2 REPLIES 2
Winfred LU
ST Employee

‎2021-01-12 06:04 PM

Just to check if MISO pins (in all the slaves) are configured as PP?

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DKari.1
Associate II

‎2021-01-13 01:49 AM

Thanks Winfred.

I made the configurations via CubeMX. I checked there and found that PA6 is configured as "alternate function push pull".

I also checked the registry and CNF6 was set to 0x2 and mode6 was set to 0x3

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