The first argument after a CJNE command can only be the Accumulator or Register 0-7. However, you can use Regs 0 or 1 to INDIRECTLY point to another location in memory.
Rather than use CJNE why not use JZ? For example;
LOOP:
MOV A,P1
JZ LOOP ; if A is all zeros, look again
...examine bits
...
...
...


Hal