Hardware SPI, strange behavior

rredding · Joined: 25 Mar 2005 Posts: 63 Location: Tacoma WA

I have an SPI vacuum fluorescent display and SPI real time clock connected to an ATMEGA8 processor. Unfortunately, the VFD likes its bits LSB first and the RTC likes its bits MSB first. So I figured I could just switch back and forth using the CONFIG SPI command and SPIINIT. The trouble is, when I have a second CONFIG SPI command anywhere in the code, even when the part of the code that contains the second CONFIG SPI and SPIINIT is not run through, the VFD stops working, getting garbled or strange text. Does anyone know why this might be happening? Any known fixes?

(Just to be sure that part of the code was not being run, I put a trap in there and the second CONFIG SPI and SPIINIT were not being run.) Things do work OK for the VFD if the second CONFIG SPI does not change the bit order.

DToolan · Posted: Sat Mar 26, 2005 11:14 pm Post subject:

Try this as a work-around. After you have initially config'd the SPI in the beginning of your program using the CONFIG statement, use the following in the rest of your program to set data order without any further config's or spi inits...

'least significant bit first
SET SPCR.5

'most significant bit first
RESET SPCR.5

rredding · Joined: 25 Mar 2005 Posts: 63 Location: Tacoma WA

Thanks for the advice. That solution worked well.