Simple Assembly Language Question

tom90

I am trying to learn assembly language by sending a control byte of 10010000 to an A/D chip.

I send:

mov outa, pin

to set the pin high for the first one.

How do I set the pin low for the next 0?
I know i can use XOR to toggle the output state, but this doesn't seem to be working very well.

in spin I would just say:
outa[noparse][[/noparse]Pin]:=0

Is there an assembly language equivalent to this?

Thanks
Tom

Mike Green

OUTA and DIRA are 32-bit registers. In Spin, you can address single bits or groups of bits in these registers. In assembly, you can only access the whole register. You have to use instructions like OR, XOR, AND, ANDN to change single or multiple bits. Typically, you'd have a constant defined that contains all zero bits except for the bit corresponding to the I/O pin you want. If PIN is a constant whose value is the number of the I/O pin, the constant can be defined as the value |<PIN. This is just a one shifted left PIN bit positions. Here are several examples:

pinMask    long  |< PIN                ' A 32 bit word of all zeros except for the bit for the I/O pin

                or      dira,pinMask      ' Set I/O pin mode to output

                andn dira,pinMask       ' Set I/O pin mode to input

                or      outa,pinMask      ' Set the I/O pin to high

                andn outa,pinMask      ' Set the I/O pin to low

                xor    outa,pinMask      ' Toggle the I/O pin

                test   pinMask,ina  wc  ' C flag true if I/O pin high

Post Edited (Mike Green) : 10/9/2007 4:13:44 PM GMT

Graham Stabler

I also cover this stuff in my 4 step assembly plan:

http://forums.parallax.com/showthread.php?p=647408

deSilva has also done an excellent tutorial on assembly that is well worth reading but I don't have the link to hand at the moment.

Graham

deSilva

tom90 said...
I am trying to learn assembly language by sending a control byte of 10010000 to an A/D chip.

Interesting approach

BradC

I tried to learn it by standing on my head while flipping the pages of the Propeller reference manual with my toes.. I think his method is probably more effective.

deSilva

Well, the proof is in the pudding

Ken Peterson

@tom90: Most people try to learn assembly by turning an LED on and off. You are ambitious!

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


The more I know, the more I know I don't know.· Is this what they call Wisdom?

tom90

Thanks for the help guys! I think i'm starting to get this to work (very slowly).