Having Trouble with PASM TEST Instruction

JonnyMac

I'm baffled over something that should be stupidly easy. This works as I expect:

testbit                 mov     tmp1, ina
                        and     tmp1, pinMask           wz
        if_z            wrlong  zero, pinStatus
        if_nz           wrlong  one, pinStatus
                        jmp     #testbit

... but this version doesn't; it always returns 0 even when the pin is high.

testbit                 test    ina, pinMask            wz
        if_z            wrlong  zero, pinStatus
        if_nz           wrlong  one, pinStatus
                        jmp     #testbit

I must be missing something but, for the life of me, have not been able to deduce what that something is....

JonnyMac

Okay, never mind -- problem solved by switching the order of operators for test

testbit                 test    pinMask, ina            wz
        if_z            wrlong  zero, pinStatus
        if_nz           wrlong  one, pinStatus
                        jmp     #testbit

This version works but as both pinMask and ina are variables I don't understand why the order matters.

Post Edited (JonnyMac) : 4/25/2009 4:42:46 PM GMT

Bill Henning

"ina" is a special register, only accessed properly when it is in the "source" part of the instruction - when in the "destination" part you access the "shadow" ram "beneath" it.

JonnyMac said...
Okay, never mind -- problem solved by switching the order of operators for test

testbit                 test    pinMask, ina            wz
        if_z            wrlong  zero, pinStatus
        if_nz           wrlong  one, pinStatus
                        jmp     #testbit

This version works but as both pinMask and ina are variables I don't understand why the order matters.

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JonnyMac

Thanks for the clarification, Bill. For as much BASIC Stamp experience as I have I should have figured that out.