checking two input pin states in assembly

ionymous · 2008-11-10 20:00

I am coding in assembly.
I have two input pins I am interested in, lets say pin 5 and 6.
The other inputs are in unknown states... I have not tied them to ground, and many are for peripherals since I'm using a development board.

I'm using "and" to mask the inputs I care about, and then "xor" with "wz" to determine if the bits I care about are set.

Here's an example:

                        mov     temp1, ina              'Get the current inputs
                        and     temp1, bothInputs       'Mask the inputs I care about

                        xor     temp1, bothInputs wz,nr 'Check if both inputs are high
        if_z            jmp     #BothInputsAreHigh             

                        xor     temp1, justInput5 wz,nr 'Check if just input 5 is high
        if_z            jmp     #JustInput5IsHigh             

        
bothInputs long %110_0000
justInput5 long %010_0000
temp1 long 0

Is this a good way to do it, or is there a better way?
Thanks
Ion

Ariba · 2008-11-10 23:23

You can use TEST, this is the same as AND with NR:


                 test    bothInputs,ina    wz,wc   'Mask the inputs I care about
  if_z           jmp     #BothInputsAreLow             
  if_nz_and_nc   jmp     #BothInputsAreHigh        'Carry is cleared if an even number of bits is set           
  if_nz_and_c    jmp     #OneInputsIsHigh          'Carry is set if an odd number of bits is set   

                 test    justInput5,ina    wz      'Check if just input 5 is high
  if_nz          jmp     #JustInput5IsHigh             
  if_z           jmp     #Input5IsLow             

' for waiting until inputs are set:
                 waitpeq bothInputs,bothInputs     'Wait until both are set
                 waitpne bothInputs,bothInputs     'Wait until one or both are cleared

The test for both inputs by the Carry works only with 2 inputs, if you have more bits, then your methode with xor is the right one.
And be aware that:
test maskreg,ina is not the same as test ina,maskreg
the second does not work as expected, because the INA has to be the source register.

Andy

checking two input pin states in assembly

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