STM32H7 PCx_C pins unusable for boundary scan?

[regjoe]

Hello,

I used CubeMX for a design for H75x in LQFP176.

I was able to configure SDCKE0+SDNE0 signals of SDRAM Bank 1 to PC2_C and PC3_C.

Now I wanted to configure a SDRAM test using JTAG boundary scan but the JTAG tool manufacturer claims that these PCx_C pins cannot be used for boundary scan.

In the BSD file STM32H743_753_LQFP176.bsd these pins are declared as "linkage bit".

PC2_C      : linkage bit;
PC3_C      : linkage bit;

In the BSD file STM32H743_753_TFBGA240.bsd for the BGA package, which has both PCx and PCx_C pins, only the PCx_C analog pins are declared as "linkage bit". 

PC2        : inout   bit;
PC2_C      : linkage bit;
PC3        : inout   bit;
PC3_C      : linkage bit;

According to DS12117 Rev 9, the LQFP176 package has PC2_C and PC3_C pins only and the internal pads PC2 and PC3 are not routed to physical pins.

According to RM0433 12.3.1 the default state after reset is analog switch closed.

IMHO this pin is a GPIO pin after reset. Due to lack of HW I cannot verify this at the moment. 

Therefore, shouldn't be PCx_C in the LQFP176 BSD file also of type "inout bit" and can be used for boundary scan?

[ELABI.1]

Hello @regjoe,

You cannot use these pins for the SDRAM. However, you can use other available options such as pin PH3 or PC4 for SDNE0 instead of PC2_C, and pin PH2 or PC5 for SDCKE0 instead of PC3_C.

There is a limitation - Errata regarding the current on these pins precisely in the section 2.2.25.

Thank you.

ELABI.1

[regjoe]

Hello ELABI.1,

too bad.

Seems that CubeMx isn't aware of this limitation.

Here you can configure Pxy_C pins for Ethernet, SPI, SDRAM, etc. and in all speed options including high speed.

IMHO the high speed option requires a drive strength >> 1mA.

I wonder if there is a chance that SDRAM works despite the 1mA limitiation.

Probably with lower clock rate.

In DS12117 rev9 Table 8 Pxy_C pins have attributes ANA and TT_a but I cannot find a documentation regarding these attributes. Second, is there any information from ST avaliable regarding "boundary scan capable pins"?

Thank you

[regjoe]

---

@regjoe wrote:

Seems that CubeMx isn't aware of this limitation.

---

Seems to me this is an well-known but not fixed bug in CubeMx

https://community.st.com/t5/stm32cubemx-mcus/bug-cubemx-should-warn-h7-users-against-pc2-c-pc3-c-pitfalls/td-p/708817 

[ELABI.1]

Hello @regjoe 

Yes, you are right. Unfortunately, CubeMX cannot display all such information.

Thank you.

ELABI.1

[regjoe]

Hello @ELABI.1 

for me, disabling the "High Speed" option or showing an extra column with the pin type "ANA" or "TT_a", as shown in DS12117 rev9 Table 8, whatever this type name exactly means, could have saved one or another from a board redesign. 

Thank you.

[regjoe]

Hello @ELABI.1 

questions remaining:

You wrote that the PC2_C and PC3_C pins are "unusable for SDRAM" due to limited current. But nevertheless, these pins can be configured by CubeMx. Does this mean that these pins can be used for SDRAM but only at lower speeds?

Second, is there any information in the datasheets which pins are not boundary-scan-capable?

Is there another source for BSD files than this one H7 Boundary Scan Files ?

BTW, I'm also looking for STM32G0B0VET6 BSD files but can't find any. Is this family not boundary-scan-capable?

Thank you

[AScha.3]

Hi,

I fell into the trap to use these xx_C pins : used one xx_C pin as SPI/data to a small TFT ;

at first everything working fine, with HAL and about 4MHz clock ;  but display update bit slow;

then i tried direct write DMA->SPI and set clock to 24MHz ; very fast now, fine -- but only about some seconds !

Then nothing more coming to TFT...pin was dead. Hmmm....

Tried remap to use other pin , working fine again - and still does.

So i killed the tiny analog switch, that connects the pin here !  (1mA output load limit , afair.)

You can imagine these pins like a "normal" pin, with a very tiny resistor in series (about 300 ohms);

as long as you use the pin as input , no problem; as an output, at low speed and hi impedance load , no problem, as long as output current < 1 mA ; more load and its toasted .

So these pins might be used for SDRAM , if low capacitative load and low speed (maybe 4MHz).

I made simu, 300 ohms and 1mA -> 0,3mW max.

4MHz in 10pF load giving : 1mA rms , so its the limit.

[regjoe]

Hello @AScha.3

thanks a lot, you saved me from another mistake. My first idea was to use these pins for "low speed 20MHz" SPI MISO/MOSI signals...

Probably I'll use these pins for driving the DE input of an RS485 transceiver chip, probably adding a 1-10k resistor in series.

I wonder why these pins can be configured as "High Speed" pins in CubeMx :(

[regjoe]

According to this information

I better use 'em as inputs. Just to make sure.