Hello everybody

This relates to 89c668 controller, P0 port.

We are facing a typical problem in 5% of our units which are manufactured using same PCB.
The PLCC socket we are using is different.
PROBLEM: The P0 data lines randomly get stuck to low for random period time.
Basically we are accessing four devises on the bus.
One (MFRC500 smartcard reader IC) using MOVX, this devises works always.
Other devise (LCD 16x2) using P0 port.
Other two are 74HC374 latches as output ports.
The P0 port has 4k7 pull up.

The devises LCD & 74HC374 start malfunctioning when ever the P0 line gets stuck low.

The observation is that any 1 or two of the 8 P0 lines shall get stuck to 0. In such case the MOVX works fine but the Mov P0 starts failing.

Same products are working in the field for over two months on contineous basis.

We have been struggling to resolve this problem for last 8 days, we have changed the controllers, 74HC374 batch, LCD batch, but without any success.

Basically under which condition the P0 port shall get stuck to zero. From software we are always outputting FF whenever a access is done.

Please spare some time to resolve the above.
N B Patil
INDIA