Yes, i've already read it since i've already made some circuits with the 89c420. But i've never used external code/data memory. On the application notes of the microcontrollers from dallas, there are some very basic circuits where they explain how to connect memory for expanding code or data space. My problem is to put toghether the circuits and use only an IC for code and data.
The connections that i think to do are:
89C420 pin--->NV-SRAM pin
A[8..15]--->A[8..15]
WR--->WR
(RD and PSEN)--->RD
PSEN--->A16
The bus is demultiplexed using the 74HC573, but my problem is on the control signals section.
So, is this correct? PSEN connected to the A16 address line is sufficient to select the lower 64k block (code space) or the upper 64k block (data space)?