LPC17XX SPI SPCR register BITEnable for 8 bits

[nicholas1]

Hi, new to embedded. I am communicating to various peripherals via SPI with the LPC1758. The first device I had working required a 32 bit word. I got this working by sending 2x16 bit words no problem.

I then moved on to the next device which required a 24bit word, which meant that 8-bit SPI transfer was better suited. I then decided to change the previous device implementation to send 4x8bit words instead.

I decided to leave the SPCR->BitEnable (SPCR bit 2)  enabled and set SPCR->BITS (SPCR 11:8) to 1000 (8 bits per transfer) and could not get the communication working.

After trying everything I disabled SPCR->BitEnable (SPCR bit 2), which set the transfer to default (8 bit transfer) and suddenly sending works fine with no other changes other than removing SPCR->BitEnable (SPCR bit 2) and SPCR->BITS (SPCR 11:8)  from the code.

Is anyone able to tell me why this may be? Didn't post any code as I am unsure if that will help.

kind regards,

Nick

[jeremyzhou]

Hi  Nicholas Lawrenson,
Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
It seems so weird, definitely, the SPI is able to support the 8-bit format after setting BitEnable bit with BITS=0x1000.
In the LPCOpen library, it provides the periph_spi demo and please refer to it for details.

https://www.nxp.com/support/developer-resources/software-development-tools/lpc-developer-resources-/...
Have a great day,
TIC

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