EPROM emulator

[steve ravet]

"Andrew K. Mattei" wrote:
> 
> Bruce Plecan wrote:
> >
> > I thinks we may be over the $50, so just one depending on price for CSH, HQ,
> > but with the staff we got here might have to get a spare, anyway.
> 
> Looking at the design I have in mind (seems like we have quite a few
> differing ideas :) ), I added up the raw costs, and it fell out at
> ~$150. :( Most of that ($90) was for the NVRAM I had in mind. (128k x 8)
> Dallas Semiconductor DS1245Y/AB. About $45/each from Newark. They grow
> on trees around here where I work (that's why I had them in mind ;^D),
> but for a "buy in" part, that's too expensive.

Drop the NVRAM.  Use a flash part and a DP SRAM.  The SRAMs can be
battery backed if desired with external parts.

Did some more looking around.  IDT (www.idt.com) makes DP RAMs also. 
They have them in 32kx8 and 64kx8, in PGA and PLCC packages which are
actually usable.  Part numbers are 7007 (32k) and 7008 (64k).  Cypress
claims pin compatibility with these parts, so for now let's assume that
there aren't any same-address collision issues to worry about.


> 
> Here's how "my" parts list broke out:
> 
> (2) DS1245Y/AB 128kx8 NVSRAMs: $90
> (1) 17C742 Microchip PIC: $21 (I think that's the part number; from
> DigiKey)

Let's try a flash PIC part, they're cheaper because they're not in a UV
erasable package.  16f874 and 16f877 look like good parts:  5 I/O ports
for 33 total bits of I/O.  2 pins of port C are for the serial port,
which leaves 31 I/O.  That's enough for 16 address lines, 8 data lines,
7 control lines.  Digikey doesn't have a price on these, I don't know if
they carry them or not.  The best part of the flash part?  A few extra
components on the emulator board makes the PIC in-circuit programmable
via the serial or parallel port.  No programmer required, only some free
software and a cable.  Makes it easier if everyone can program their own
parts.

The rest of my price list is probably similar to yours, except fewer
muxs/tri-states.  Also, based on other group buys the board will
probably be cheaper, like the $15 range.

I'm working on a schematic to illustrate it....

--steve

> (12) 74HC245 Tri-state octal bus: $12
> (1) 74HC125 Tri-state quad bus: $1
> (1) Printed circuit board: $25 (?)
> (misc stuff): a few more $ ;)
> 

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com