Port alias in Port Expanders (MCP23S17)

[ecoli-557]

Henrik-
Also forgot to mention that in the older I2C design I had 8 bits of inputs and 8 bits of outputs on one 2317.
This new design is all outputs - I thought it would be easier!
Not so much......
Regards,
Steve

[HenrikOlsson]

Sounds like what you're looking for is the DCD operator:

DCD returns the decoded value of a bit number. It changes a bit number (0 - 31) into a binary number with only that bit set to 1. All other bits are set to 0.
B0 = DCD 2 ' Sets B0 to %00000100

So, perhaps something:

OutBits VAR WORD
  GPA VAR OutBits.BYTE0
  GPB VAR OutBits.BYTE1

Outbits = DCD $E

Henrik.

[ecoli-557]

Thanks I will try that!

I have made some progress but I still need a way to get from 1 byte which will tell me which of the 16 outputs to turn on.

Current test code:

                      OutA=$FFFE                                        'Initial value for word var                      
                      OutA_hi=OutA.highbyte                             'Splits into hibyte
                      OutA_lo=OutA.lowbyte                              'And into low byte of the word var
                      OutA_lo.3=0                                       'Bit mod
                      OutA_hi.5=0                                       'Another bit mod
                        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

This gives me what I want - EXCEPT - for that I have to resolve 1 byte into a word and figure out how to get the pointer right........
starting with a byte var which has a value from 0-15 to a specific bit on the MCP23S17 still evades me I am afraid.

[ecoli-557]

Henrik-
Thanks for the assist, but I don't think I can use that idea. There are some outputs which will be already active which another serial command comes in and I will need to add to the already ON LEDs with whatever new ones are called for.
There is a serial comm line coming into the project and on that serial comm is a byte which will let me know which output(s) to turn on. Some may or may not be on.
So, I will have to logically AND them to get the correct outputs on when they need to be.

[ecoli-557]

Why does this not work?
OutA.12=0 doesn't gen an error but it nor the other (OutA.15=0) turns ON an LED?????

                      OutA=$FFFE                                        'Initial value for word var                      
                      OutA_hi=OutA.highbyte                             'Splits into hibyte
                      OutA_lo=OutA.lowbyte                              'And into low byte of the word var
'                      OutA_lo.3=0                                       'Bit mod - WORKS
'                      OutA_hi.5=0                                       'Another bit mod - WORKS
                      OutA.12=0      'Why doesn't this work?
                      OutA.15=0      'Or this?
                        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

[richard]

OutA_hi=OutA.highbyte 'Splits into hibyte
OutA_lo=OutA.lowbyte 'And into low byte of the word var

is a simple assignment operation not an alias

OutA=$FFFE 'Initial value for word var
OutA.12=0
OutA.15=0
OutA_hi=OutA.highbyte 'Splits into hibyte
OutA_lo=OutA.lowbyte 'And into low byte of the word var

would fix it (get the order correct)

[ecoli-557]

Thanks!
I tried your suggestion:

                      OutA=$FFFF                                        'Initial value for word var                      
                      OutA.0=0                                       'Bit mod - WORKS
                      OutA.2=0                                       'Another bit mod - WORKS                      OutA.0=0                                       'Bit mod - WORKS
                      OutA.8=0                                       'Another bit mod - WORKS
                      OutA.10=0                                       'Bit mod - WORKS
                      OutA.12=0                                       'Another bit mod - WORKS
                      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

And it works like a CHAMP!
However (you knew it might come) how do I resolve a single byte variable which tells me which bit to turn on/off into a word var?
My need for this home project, is to read a byte var and based on its value turn on/off a bit on the expander?
Example: Var=$C, so I need to turn on the 12th bit on the expander.
Regards,
Steve