Hi,

I've begun testing the T89C51AC3 and a replacement part for out T89C51AC2. I've received my first batch of samples w/ the AC3 and I am having an issue. I cannot program to the machine using Atmel's ISP. I've checked the necessary signals, PSEN, EA, RESET, and ALE, they are all correct however it won't allow me to program.

When I checked the crystal I noticed that the O/P of the board with the T89C51AC2 had a peak voltage of 4.6V, while the T89C51AC3 has a peak voltage of 3.6V, is this normal?

Also the T89C51AC2 and AC3 are pin for pin compatible, with the biggest differences being that the AC3 has double the RAM and Code Memory as well as internal black-out protection on the AC3. We had external black-out protection on the AC2, and that remains in the current design.