SPI using picaxe

Tonight is the first time that i have successfully used the SPI protocol with a Picaxe chip (not on a 28X1 or a 40X1 that have it as part of their software library). To be honest, i hadn't tried before today - just didn't get around to it. But this is really a useful thing. In the example code below, i controlled the resistance of one of the pots on an MCP42100 IC.

The picture above shows outputs 0, 1 and 2 of the Picaxe 08-M being used as the CS (chip select), SCK (spi clock) and MOSI (master out, slave in) lines. There is no MISO (master in, slave out) line because the Picaxe chip can only write to the digital pot (as opposed to being able to read from it).

It really has been a productive evening. This would not have been possible without P. H. Anderson's page on using SPI with the Picaxe chips (a true master!). Thanks.

[expand / collapse code]

#rem

** SPI PROTOCOL AND PICAXE TEST **



by Sebastian Tomczak

19 July 2007

Adelaide, Australia

#endrem



; Setup

symbol CS = 0 ; set chip select pin

symbol SCK = 1 ; set spi clock pin

symbol MOSI = 2 ; set master out, slave in pin



symbol cmd_byte0 = %00010001 ; write to pot 0

symbol dat_byte0 = b0 ; data output for pot 0

symbol work = b1 ; working byte

symbol counting = b2



; Program



main:

let dat_byte0 = dat_byte0 + 1



low CS



let work = cmd_byte0

let counting = 0

for counting = 0 to 7

if work > 127 then spi_high1

low MOSI

goto spi_out1

spi_high1:

high MOSI



spi_out1:

high SCK

let work = work * 2

low SCK

next



let work = dat_byte0

let counting = 0

for counting = 0 to 7

if work > 127 then spi_high2

low MOSI

goto spi_out2

spi_high2:

high MOSI



spi_out2:

high SCK

let work = work * 2

low SCK

next



high CS



goto main