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PIC Microcontoller Range Check Math Methods

Test if a value is in a certain range

W = value

addlw 255 - Hi
addlw (Hi - Lo) + 1

Carry is set if W is in range Lo - Hi

It works for all values of Hi and Lo although it is not optimal for 255 and 0. It even works for ranges that wrap around 255 back to 0. For instance, if you set Lo to 240 and Hi to 15, it will match 0..15 and also 240..255. And it works for signed numbers. You can set Lo to -3 and Hi to 5 to match -3..+5.

The only requirement is that your assembler must truncate literals to eight bits. If not, you can still use it by masking the literals yourself:

        addlw (255 - Hi) & 0ffh
        addlw ((Hi - Lo) + 1) & 0ffh

For example:

Lower = 50
Upper = 60

addlw 255 - Hi equates to addlw 195
addlw (Hi - Lo) + 1 equates to addlw 11

W = 50          ; lower limit

addlw 195       ; w = 245
addlw 11        ; w = 0, C = 1, result = OK

W = 55          ; in range

addlw 195       ; w = 250
addlw 11        ; w = 5, C = 1, result = OK

W = 60          ; upper limit

addlw 195       ; w = 255
addlw 11        ; w = 11, C = 1, result = OK

W = 49          ; under minimum

addlw 195       ; w = 244
addlw 11        ; w = 255, C = 0, result = Not OK

W = 61          ; over maximum

addlw 195       ; w = 0
addlw 11        ; w = 11, C = 0, result = Not OK



Ondrej Zoubek Says: " please note, that 12-bit core (PIC16C5x, 12C5xx) has no addlw instruction " +

Code:

See also:


file: /Techref/microchip/rangechk.htm, 4KB, , updated: 2009/4/10 13:37, local time: 2017/4/27 07:56,
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