Hi
We're trying to interface a PIC micro to an 8052 micro using the Parallel Slave Port on the PIC. The 8052 can read bytes written to it by the PIC ok, but when the 8052 writes to the PIC, the PIC tends to read what it last wrote and not what the 8052 sent. The voltage levels on the data bus show contention with "half levels" when the PIC and 8052 are opposite states.
Is there something that has to be set differently in the PIC when it's in "read mode" than when it's in write mode?
TIA
Which PIC are you using ??
Please show your work. Schematic ??
I too have interfaced the PSP to a 8051 buss without problems.
What does you PIC code look like ??
donald
It would seem that you are driving the bus with both devices at the same time. The problm arises beause you have 2 masters. You need to devise some sort of syncronisation or protocall system to determine who has control of the bus at any given time.
It turns out a bug in the PIC software was clobbering the IOPort setup. It took a while to track down. Now it's working fine.
Thanks for the reply.
Hi darkknight, How are you notifying the 8052 that the byte is ready / has been read? It seemed to me that the external flag system to the bus was poorly supported. Regards Rocky
We use a "manually" controlled signal that connects to the EXT 0 interrupt pin on the 8052 and the PIC software drives it high then low to tell the 8052 that a byte is ready or has been read. The data sent between the two micros is multibyte messages and each message indicates which micro will transmit next after the current message. One single lost (or possibly corrupted) character and the link dies - upon which the 8052 reboots both micros.
darkknight
thanks for the feedback
Rocky
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