Interfacing uPSD3253B to the databus of another microcontroller

info81 · ‎2005-08-22

Posted on August 22, 2005 at 11:00

info81 · ‎2011-05-17

Posted on May 17, 2011 at 12:08

I cannot figure out if it is possible to define a I/O-pin connected to the CPLD to act both as an input and as an output.

What I want to achieve is making it possible for another microcontroller (a Hitachi H8) to fetch and leave data to a port on the uPSD using the other controllers databus and the other controllers CE, RE and WE signals. In other words, combining a latch controlled by external WE with a buffer controlled by external RE on the same pin (letting the uPSD act as a type of memory to the H8).

Can anyone, with more experience with the uPSD than me, please tell me if this can be done?

jdaniel · ‎2011-05-17

Posted on May 17, 2011 at 12:08

Magnus,

The best way to do this is to use a ''dual-ported RAM.'' This is basically a RAM chip with two separate address/data buses that connect to the same internal memory. They also have some arbitration and special registers that help the two processors coordinate their activies. Cypress Semi makes a pretty decent line of DPRAMs and I've used one of them successfully with a uPSD in a design.