A simple question..

[Craig Pugsley]

Hi there,

I've got a simple (dumb) question to finish off the week.

With memory chips (Eprom / static ram), can you just tie the chip select
lines to ground (!CS ---> active low inputs), presuming you only have
one of each.

IE will the outputs all be tristate unless it's reading or writing.

I ask this as the chip I'm using (80C552, from 8051 family) outputs the
same memory address range for the ROM and RAM, with 3 control lines:

No. 1 --> Read the program memory (IE the EPROM, this signal is !PSEN)
No. 2 --> Read the data memory    (IE the RAM,    "     "    "  !RD)
No. 3 --> Write to the data memory(IE the RAM,    "     "    "  !WR)
                                               
IE, you can read location 1234 in EPROM with the !PSEN signal active,
or   "   "   "      "      "   "  RAM    "    "  !RD     "      "
                   __
For me to derive a CS input for each memory device would be a major
pain, so do I need it or can I just always have them selected?

Also, what do you need to do turn a RAM into a non-volatile?
Just disable the !WR signal when voltage drops below 4.8ish volts, so
the micro going haywire won't write over the ram? (Obviously with a
battery / diode arrangement to keep power on the ram),

OR would it just be easier to use a proprietary (eg DALLAS) nvram module,
or maybe even flash eeprom? Assume data won't change much.(Maybe 2 or 3
writes max per day).

Craig.

pugsley at trl.oz.au