89C668H overprogram

[microappl]

I designed a product using 89C668H.
I find a programming yield problem using FM 1.84.
On about 20% of the 668's the chip will jump to a random location and crash while executing the main idle loop.
The failing chip(s) verifie(s) under FM.

If I overprogram the failing chip without erasing it two or three times, this seems to solve the problem.

This would seem to indicate that the 668 ISP programming code has a problem.

[erik malund]

just a guess.  Do you have P2.7 AND P2.6 helke high

Erik

[Andy Ayre]

Sounds like an electrical problem. Do you have gitches or ripple on the power supply or RST pin? What about the XTAL pins? What is the voltage actually at the VCC, GND and RST pins? Does the signal at the XTAL pins look ok?

[erik malund]

Do you have Vpp directly to +5?

Erik

[udj]

I am using 89C668H. product
I find a programming problem flash programming.
Chip is responding fro  ISP communication what will be the problem

This would seem to indicate that the 668 ISP programming code has a problem.

[Andy Ayre]

Can you elaborate on "Chip is responding fro ISP communication what will be the problem"? What are you observing?

Did you let P2.6 and P2.7 float or pull them high?