Interfaceing another PIC? Replacing a existing Digital chip with My PIC

[HenrikOlsson]

Where does it say that the old chip is running on 7V?

You can do it with a PIC (though a 4550 for this seems overkill as have been said) but you need to know what the clock frequency and "data update rate" of the communications are. Not for setting anything up but in order to decide HOW to do it with the PIC.

If the clock frequency is low enough you may be able to grab the data by using the latch signal as a sync and then poll the clock and data signals in a loop. If the clock frequency is too high for that you should be able to set the MSSP module up as a SPI slave, probably have to think a bit about how to do the sync. It would help with a scope or logic analyzer shot of a "frame" being transfered from the main board to the display board.

What type of LCD are you talking about, a "standard" HD44780 based display or something else?

/Henrik.

EDIT: You would emulate a shift register because that's what's inside the LED driver chip on your original board.