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problem using SAI block B on STM32F427VIT6 (100 pin LQFP)

Question asked by galens on May 24, 2015
Latest reply on May 25, 2015 by galens

I've been trying to use the SD_B output on an STM32F427VIT6 with no success.  This is the 100 pin package.  With typical SAI usage, SAI block B would not be usable since the MCLK, SCLK, and FS pins are on port F, which is not pinned out on the 100 pin package.  However, for my application, all I need is the SD_B output.  I was planning to use SD_B to create a custom pulse train, where SD_B would be the only output (no MCLK, SCLK, or FS needed).

To experiment with the SAI, I took the STM324x9I_EVAL SAI_Audio example from the STM32Cube_FW_F4_V1.5.0 release and tweaked it to run on a board that has an STM32F427IGT6 (176 pin LQFP).  When I run my code on this board, all outputs behave as expected.  The code configures the GPIO such that both of the possible SD_B pins are driven (PE3 and PF6), and that is the behaviour I see.  PE3 and PF6 are identical and are shifting out audio sample data.

When I take the identical code and program it into the STM32F427VIT6, port PE3 does not toggle.  If I use a debugger to read the GPIOF input data register, I don't see any input activity.  When I read the GPIOF input data register on the 176 pin device, I can see all of the associated SAI B pins toggling.

Note that I have tried this same experiment, but with SAI block A.  The SAI block A pins are on ports D and E, which are available on both the 100 and 176 pin devices.  In this case, both devices perform as expected, driving MCLK, SCLK, FS, and SD, with SD appearing at both PD6 and PE6.

Both the 100 and 176 pin devices appear to be rev Y.

To summarize, I was expecting the 100 pin and 176 pin devices to behave the same with respect to SAI SD_B, but that does not appear to be the case.  Are the unbonded GPIO ports on the smaller packages disabled in some fashion?  Why is SAI SD_B at PE3 not functioning in the 100 pin package?