I'm working on my home project of building the 8-bit computer and now I'm on the RAM building stage. I'm going to use this chip for as my RAM UTRON UT62256C (datasheet). This chip is to be connected to the common bus, to which 8-bit registers are connected through 3-state buffers. My question is about write cycle timings (see the diagram below)
The doc says that after !WE goes down there is a period of time twhz when signals on I/O pins must be not applied: "4.During this period, I/O pins are in the output state, and input signals must not be applied. "
Question #1: Does that mean that I CAN NOT set-up the data upfront and then just put the !WE low for some period of time? If I do so, will it damage the chip?
Having said that !CE is to be always LOW, I assumed that my write cycle could look like this:
- Set up the address using
- Set up the data on the bus
- Make !WE low for certain period of time.
As it's an educational project I wanted write cycle to be like this because it simplifies design for manual mode of putting data to the SRAM. I was going to use dip switchers to set up the data and the address and one button to move !WE from High to Low maybe with 555 timer to set-up the pulse length.
Question #2: If I must not put the data on I/O pins before twhz, I was thinking about could you please advice some circuit that will allow to do manual programming with dip switchers
I was thinking about adding 3-state buffer between I/O pins and the dip switchers and some circuit that generates two pulses with the right timings triggered by pushing the button:
- First !WE goes down for certain period of time for example 555 timer could be used.
- !WE pulse triggers the second 555 timer that generates !OE pulse on the 3 state buffer.
Thanks for you replies in advance.