EPROM emulator

[steve ravet]

> Ahh... ;) Well, that's what happens when engineers get stuck in the
> marketing department. OK, how about NVSRAM? I have a Benchmarq BQ4015
> sitting on my desk at work. It's a 4Mbit module. Here's my concern. I'd
> like to leave the Eprom Emulator plugged in to the car. All the time. ;)
> Not have to load it first - when I feel like tinkering, I plug in to the
> RS232 port, tweak a few parameters, and then disconnect the laptop.
> That's why I was thinking EEPROM... or Flash... or NVSRAM...

I think a flash chip and a dual port SRAM would do the trick.  The dual
port eliminates problems keeping two different RAMs coherent. 
Simultaneous access to the same address probably isn't a problem as long
as you're only changing the data and not code. The functions that the
PIC would do (under control of the PC) are:

1)  receive data from the serial port, write it to the RAM
2)  switch OE between the RAM and multiple flash images.
3)  copy RAM image to flash.
4)  dump any image back to the PC.
5)  others?

It would be nice if 2) and 3) could be done via switches on the board. 
Also nice would be LEDs to indicate which image is running the engine,
and if the RAM has changed since being committed to the flash.


> Seems, though, that we'll need a pretty big PIC to handle all the
> address and data parallel to serial conversion... Looking at Digi-Key,
> looks like the PIC17C42/43/44 might fit the bill... 33 i/o pins... :)
> Still under $20, though.

The conversion happens in hardware.  The PIC has a real UART in it,
which means reading serial data is just reading from an internal port. 
No big deal, believe me.

I still don't see the need for the address and data muxes mentioned
before.  Does everyone think this simple OE scheme would work?

--steve

-- 
Steve Ravet
ARM, INC
steve.ravet at arm.com
www.arm.com