Port alias in Port Expanders (MCP23S17)

[ecoli-557]

OK, it is working!
Thanks to all who helped and provided some food for thought.....
Code below for any others who need to do this:

                      OutA=$FFFF                                        'Initial value for word var - everything is OFF                      
                      PortDevice=$A                                     'Var from comm link
                      OutA.0[PortDevice]=0                              'This works!
'                      OutA.2=0                                          'Manual bit mod - works though  
'                      OutA.12=0                                         'Manual bit mod - works though
                      OutA_hi=OutA.highbyte                             'Splits into hibyte
                      OutA_lo=OutA.lowbyte                              'And into low byte of the word var
                        OutA_MCPReg = OLATA                             'Sets up PORTA output
                        OutA_DataOut=OutA_lo                            'Sets up data to be pushed to the MCP23S17 as the low byte
                        gosub SEND_OutA_2317                            'Send it
                        pause 10                                        'Wait a bit
                        OutA_MCPReg = OLATB                             'Sets up PORTB output
                        OutA_DataOut=OutA_hi                            'Sets up data to be pushed to the MCP23S17 as the hi byte
                        gosub SEND_OutA_2317                            'Send it

Happy New Year!
-Steve

[richard]

OutA var word


asm

OutA_hi=OutA
OutA_lo=OutA+1

endasm

OutA_hi var byte EXT
OutA_lo var byte EXT

the easy way

ps I hope I got the endianness correct if not swap the hi byte low byte definitions

[richard]

yep I did get it wrong (choice of two I will pick the wrong one every time)

found my endianness note

MyVar =$AABB would be stored little-endian. I.E. if the address
of MyVar starts at 30h, then $BB will be stored at 30h followed by $AA at 31h


so

asm
OutA_hi=OutA+1
OutA_lo=OutA
endasm

[ecoli-557]

Thanks, I will give that a try.
Now if I could write both bytes at the same SPI communication, that would be an even bigger win!

[tumbleweed]

If you have the MCP23S17 IOCON register set to it's default setting of $00 that sets the chip to 16-bit mode (BANK=0) with auto address increment enabled (SEQOP=0).

In that mode you can send register address byte = $14 (OLATA) and then write the two data bytes and they'll go to OLATA and OLATB.

[ecoli-557]

That is exactly what I was looking for!
I thought I had done this before but could have been mistaken.
Will try later this evening.
Thanks!
-Steve