Port alias in Port Expanders (MCP23S17)

[ecoli-557]

Henrik-
I may have been too hasty in my description ( I am back on my home project) as I am stumped. I had used the I2C version of this part a while back and have it working. Now I am trying to use the SPI version (MCP23S17) for its speed and I can't seem to figure out how to get from a byte indicating which bit to turn on for the MCP23S17 part.
Lets say I receive a var and it's value is $E. This var needs to tell the MCP23S17 that the 15th output should turn on. Now that is GPB-7 on the MCP23S17.
I have a routine that converts HEX to DECIMAL (thanks to this forum years ago) and that works fine, how to I get a single decimal to go to the correct port on the MCP23S17?
My code works fine to send a binary string (easier to visualize for me) to the MCP23S17 but I can't seem to get the finesse of going from 1 hex or 1 dec char to the right bit output.
I have looked through the forum and I have seen yours and others pointing to OUT.0[var] which gets to the VAR-position of the OUT variable but as I have 2 eight bit outputs I am stumped......

From the MCP23S17 datasheet it looks like it may be addressed as one 16 bit output, is that accurate? Any suggestions?
Some code below:

OutA var byte

OUTtest:'------------ TEST
                      OutA=$1                                                  'Simulate number from serial comm, example '1'
                      K=OutA                                                   'Sets up the conversion from hex to decimal
                      gosub H2D                                               'Performs the conversion
                      debug "After H2D K=",dec1 K,13               'Double-check what the sub did
                      k=k-8                                                        'try this for a pointer
                      OutA_DataOut=OutA.0[k]                        'Try to set the correct bit out of 8 to turn on and pass to OutA_DataOut which is passed to the MCB23S17
                        OutA_MCPReg = OLATA                             'Sets up PORTA output
'                        OutA_DataOut=%11111110                    'This works by setting individual bits, but not good for what I want to do
                        gosub SEND_OutA_2317                         'Send to the expander
                        pause 10                                               'wait a bit
                        OutA_MCPReg = OLATB                             'Sets up PORTB output
                        OutA_DataOut=%01111111
                        gosub SEND_OutA_2317

[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)