SPI for DAC MCP4802 on ATmega328p

[jabcam]

Hi all!

For reference here are two words I use to communicate with an external DAC on an Arduino R3. This is my first forage into inlining conditional AVR-assembly in Forth. PORTB is set all output elsewhere.

Cheers
/Micke

(Update: sorry about the lack of indentation. The editor apparently does not acknowledge spaces...)

\ 8-bit DAC routines
-mcp48x2
marker -mcp48x2

$4c constant SPCR
$4d constant SPSR
$4e constant SPDR

\ SPCR = 01010000 and double speed

spi-init
$50 SPCR c!
$01 SPSR c! \ double speed fosc/2

;

\ Prepare data and send with 8-bit DAC MCP4802

DAC ( u --- )
[ R24 swap, ] \ 4 lshift
[ R25 R24 mov, ]
[ R25 $0f andi, ]
[ R25 $10 ori, ] \ $1000 or
[ PORTB 2 cbi, ] \ SS on device low
[ SPDR R25 sts, ] \ Send 1st byte
[ begin, ] \ wait for SPIF, SPDR bit7
[ R25 SPSR lds, ]
[ R25 $80 andi, ]
[ mi, until, ]
[ SPDR R24 sts, ] \ Send 2nd byte
[ begin, ] \ wait for SPIF
[ R24 SPSR lds, ]
[ R24 $80 andi, ]
[ mi, until, ]
[ R24 Y+ ld, ] \ drop
[ R25 Y+ ld, ]
[ PORTB 2 sbi, ] \ SS on device high

;

[Mikael Nordman]

You can format the code in a code block with \</> or ctrl-alt-C /Micke

\ 8-bit DAC routines
-mcp48x2
marker -mcp48x2

$4c constant SPCR
$4d constant SPSR
$4e constant SPDR

\ SPCR = 01010000 and double speed
: spi-init
  %0101.0000 SPCR c!
  %0000.0001 SPSR c! \ double speed fosc/2
;

\ Prepare data and send with 8-bit DAC MCP4802
: DAC ( u --- )
  [ R24 swap,       ] \ 4 lshift
  [ R25 R24 mov,    ]
  [ R25 $0f andi,   ]
  [ R25 $10 ori,    ] \ $1000 or
  [ PORTB 2 cbi,    ] \ SS on device low
  [ SPDR R25 sts,   ] \ Send 1st byte
  [ begin,          ] \ wait for SPIF, SPDR bit7
  [   R25 SPSR lds, ]
  [   R25 $80 andi, ]
  [ mi, until,      ]
  [ SPDR R24 sts,   ] \ Send 2nd byte
  [ begin,          ] \ wait for SPIF
  [   R24 SPSR lds, ]
  [   R24 $80 andi, ]
  [ mi, until,      ]
  [ R24 Y+ ld,      ] \ drop
  [ R25 Y+ ld,      ]
  [ PORTB 2 sbi,    ] \ SS on device high
;

[jabcam]

Thanks for the tip!

And an ever bigger thanks for the Flashforth! It really is a clever environment. I'm having a ball with it. Currently I am investigating if signal processing can be done with the ATmega's meagre speed. I use ff for logical structure and ease of programming and code critical words in assembler. If I get any results I will post them here too.

/Micke (SM5JAB...)

[Mikael Nordman]

Thanks for the code.
There has been requests for Atmega assembler examples, and your code is really good.

Keep them coming !

fe value isy
ff to isy
:-)