topic Re: LPC18xx SSP0 peripheral reading only high in LPC Microcontrollers

LPC18xx SSP0 peripheral reading only high

michael_tao — Wed, 08 Jan 2020 22:31:29 GMT

Hi all,

I'm currently working with the SSP0 peripheral on a LPC1857 and a LPC1837. On both chips, I've not been able to get the MISO line to read anything besides a high value (255) no matter what is written to the line. I am able to read the correct values however when the loopback is enabled or when I use the SSP1 peripheral. I've tried getting the receive data through the DMA peripheral as well with similar results. As far as I can tell, the receive FIFO is only ever receiving a value of 255. Here are a few things I've tried:

Examining the SSP0 CR0 register to see if it is set up correctly
Examining the SCU configuration register for the MISO pin to make sure it is on the correct function
Switching the MISO pin to multiple different pins using the SCU

All the other lines (MOSI, CLK, SS) work as expected.

I have attached an example program I have written to demonstrate the misbehavior, the program simply sends 1 byte with value 100 over SPI and reads 1 byte. If you tie the MISO and MOSI lines together, one would expect a byte of 100 to be read. However, this only works with SSP1; SSP0 shows that the value 255 has been read. If you enable the loopback on SSP0 however, it works as expected and you read a value of 100.

Any help would be appreciated, thanks!

Re: LPC18xx SSP0 peripheral reading only high

michael_tao — Thu, 09 Jan 2020 16:32:50 GMT

Update: I've figured out the problem (after posting the question naturally). Turns out PF_2 was at some point being set to function 2 which is also SSP0_MISO. I'm not sure where this is happening as it's not in any of the BSP code or my code, but after setting PF_2 to the default func 0, SSP0_MISO now works on my desired pin setup.

Re: LPC18xx SSP0 peripheral reading only high

bernhardfink — Thu, 09 Jan 2020 16:51:25 GMT

Yep, also described here in this thread: https://community.nxp.com/thread/462334

If you don't do anything on the pin configuration, maybe the BootROM code configures this pin.

Regards,

Bernhard.