Hi Sam,

Lets clear up a bit.

There are only 3 CLR instructions known to the native 8051 mankind:

CLR A - wipes off the accumulator contents and leaves 00
CLR C - Knocks off the carry bit
CLR bit - Knocks off the "bit" that is defined by you.

All your CLR ACC and CLR B belong to the third category and you, as the programmer, have to define what ACC and B represent and kindly note these can only be "bits".

So when CLR ACC and CLR B do what they have done, as claimed by you, there is nothing weired about it. To clear B use "MOV B, #0"

Suggest spend some time to get a overall picture of the instruction set suummary from the link given by Andy.

Raghu