I found an interesting timing problem when trying to substitute a P89V51RB2 for a P89C51RB2.

We do some digital signal processing in real time which requires careful counting of the instruction cycles. The same code that works OK the P89C51RB2 does not run correctly (at the same speed) as the P89V51RB2. I have not taken the time to see which instuctions differ in speed but the DSP routine in question uses only addition, subtraction, MOV bit and a DJNZ instructions along with some NOPs for timing.

All other functions of the product seem to work as expected.

Cheers,

Bert van den Berg