Hi,

Can anybody confirm that parallel programming will perform a chip erase on a AT89C51RB2? I can't get it to work.

SEE BELOW for the gory details:

I've currently built a AT89C51RB2 circuit using ISP and FLIP and tried and failed to execute code from external flash.

I have been able to write to external flash and read/confirm from those areas in external flash.

The data sheet for the part described a default setting from the factory concerning the HSB in that it is set with the highest security setting, security setting level 4 which does not allow external program execution (Why did they do that!).

The data sheet also says that the only way to change the HSB is through the use of a parallel programmer.

I've constructed a parallel programmer based on an application note from Atmel and have successfully read the signature bytes.

It won't do a chip erase however.

The readings at the function and control pins are correct.
RST - 5V
PSEN - 0V
PROG - 5V before pulse
EA - 5V
P2.6 - 5V
P2.7 - 0V
P3.6 - 0V
P3.7 - 0V

I am providing a >= 10msec negative edge pulse on the program pin.

EA/Vpp is at 5 volts which is what is mentioned in the data sheet. The chip generates the correct programming voltage internally.

I am running at 6MHz on X1/X2.

Because I've had no success with this, I built a dedicated socket and hardwired all of the correct levels to the control and functions pins listed above. I placed a momentary switch on the PROG pin with debounce. It still will not perform a chip erase.

I've grounded all of the address and data pins.

??????