strange read with a 6502...

I have a problem with a read with a 6502

I read a data on a register (from a CH376S)

I have the following code:

                     *= 2000
readdata      LDA    CH376data
                      RTS


this code always get  the wrong value

                     *= 2001
readdata     LDA    CH376data
                      RTS


now with this code I get the right value...

I have a diffent result with a 6502 from:

mos technology    sometimes good (even addresses) / always good
rockwell                 always bad (even addresses)  / always good (odd 
addresses)
WDC                      not working both cases
bulgarian clone    not working both cases

any idea ? I dont really know what to think...






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