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Question asked by Tsai MingFeng on Aug 2, 2017

Hi, I have one re-flash problem with MCU MPC5746C, and my circuit almost like following picture, MCU is MPC5746C and the CAN transceiver is UJA1169. there has one resistance (0ohm) on the Reset pin between MCU and transceiver.

At start, I didn't implement any SPI function to control UJA1169, so it is working on  Forced normal mode, during debug and re-flash MCU, once UJA1169 keep in Forced normal mode (no communication via SPI), I can re-flash MCU by CYCLONE UNVERSAL, even the  resistance (0ohm) is there.


But when I implement the SPI control function for UJA1169, reset ->standby->normal->sleep->reset, and re-flash it into MCU, my module is working good, it can go to sleep/re-wakeup/CAN communication, but the problem is coming at same time.


The problem is: I can not re-flash MCU any more, when I try to use the JTAG to re-flash my module, the reset pin will keep low, I believe is the UJA1169 control it goes to LOW, because with I remove the resistance (0ohm), I can re-flash MCU normally.


Is any way can fix this re-flash problem when the resistance (0ohm) is there?

Also, I have feedback this issue to my supplier, my supplier told me that I need another chip on the reset pin between UJA1169 and MCU, like following picture, and it is came from demo board S32K144EVB-Q100.




Is there any solution can fix this issue even keep 0omh there?