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EPROM Emulator

MicroCoreLabs

Experienced Member
Joined
Feb 12, 2016
Messages
119
Hi,

I thought I would share my small EPROM Emulator project: https://microcorelabs.wordpress.com/2021/03/20/eprom-emulator/

It's a small circuit board which contains buffers to allow a Teensy 4.0 (Arduino type of board) to emulate most of the 27Cxxx EPROMS. It appears to work in a PCjr and next I will try in an XT.

I needed an emulator to do some tinkering with the IBM XT BIOS, but maybe someone here may find it useful.

Thanks,
-Ted
 
Last edited:

Ruud

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Nov 30, 2009
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796
Location
Heerlen, NL
What struck me: small! Nicely done and I'm looking forward to the Github link. Please keep us informed!
 

MicroCoreLabs

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Joined
Feb 12, 2016
Messages
119
What struck me: small! Nicely done and I'm looking forward to the Github link. Please keep us informed!

Funny... You were exactly the person I was thinking of as someone who could use this! :)

Did you use a similar emulator for your diagnostic rom work? Or programmed EPROMs for each iteration?
 

MicroCoreLabs

Experienced Member
Joined
Feb 12, 2016
Messages
119
The C code, schematics, and PCB files are now on GitHub: https://github.com/MicroCoreLabs/Projects/tree/master/EPROM_Emulator

In theory, this board could also be used to trigger on a sequence of addresses and then print something out of the UART. It could also report the progress the BIOS makes during self-test; similar to a POST board. In addition, if the history of addresses was also stored in a buffer, then if BIOS detected an error we could print the addresses that led to it...
 

hanso

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Dec 26, 2007
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Location
The Netherlands
Interesting! Really like the small footprint. Question about the 74LS245 in the circuit, what is the 245 type you used? HC?
 

Ruud

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Nov 30, 2009
Messages
796
Location
Heerlen, NL
Funny... You were exactly the person I was thinking of as someone who could use this! :)

Did you use a similar emulator for your diagnostic rom work? Or programmed EPROMs for each iteration?
I first placed a 32-pin socket plus converter to 28 pins in the original socket and then used 29F010 EEPROMs to test things. Not the fastest way but much much faster than EPROMs.

In the mean time I created my own emulator. This page isn't up to date, it doesn't mention yet that I want to use an Arduino instead of a LPT port. But you design is much neater than mine, just the very small size is a feast to the eyes!
 

atg

Member
Joined
Oct 31, 2018
Messages
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Location
East Coast US
This is great. I will follow this thread.

I am light on cash right now, and my solution to not having the diagnostic rom for the 5150 is to use an FPGA to emulate it. We shall see how that goes...
 

psergiu

Member
Joined
Dec 17, 2020
Messages
11
Location
Texas
Could this be used in a PCjr cartridge ?
Can it hold multiple 64k images and switch between them (rotary selector connected to any spare GPIO pins) (most likely will require a Teensy 4.1 as your design uses ALL 24 Teensy 4.0 pins)
32 in 1 multi-game Cart for PCjr :) :)
And with Teensy 4.1 it could even load the ROM images from the microSD.
See: https://www.raphnet.net/electronique/pcjr_cartridge/index_en.php
 

MicroCoreLabs

Experienced Member
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Feb 12, 2016
Messages
119
Could this be used in a PCjr cartridge ?
Can it hold multiple 64k images and switch between them (rotary selector connected to any spare GPIO pins) (most likely will require a Teensy 4.1 as your design uses ALL 24 Teensy 4.0 pins)
32 in 1 multi-game Cart for PCjr :) :)
And with Teensy 4.1 it could even load the ROM images from the microSD.
See: https://www.raphnet.net/electronique/pcjr_cartridge/index_en.php

Yup, totally could!

Switching ROMs could possibly be done in other ways so a Teensy 4.1 would not be necessary... Maybe use a menu accessed through UART communication with the Teensy 4.0... Or perhaps have the Teensy snoopy for write accesses to a particular address or sequence of addresses to switch the ROM image.

But yes, if a Teensy 4.1 was used we could have a physical switch and all ROM images could be stored on he microSD or in the 1MB of Teensy ROM. No software or special BIOS would be needed to run on the PCjr to access, load, or switch the images...
 

pbirkel@gmail.com

Experienced Member
Joined
Apr 7, 2013
Messages
497
Location
Silver Spring, MD, USA
Question about the 74LS245 in the circuit, what is the 245 type you used? HC?

Ok, the BOM is uptodate!

Where is the BOM located, please? I don't see it in GitHub. The schematic states 74LS245 but specifies 3.3VDC. Your web pages states "SMT buffer". The visible markings on the eBay listing are nondescript (or at least indecipherable by me); LX2458 doesn't seem to correspond to any TI part.

My best guess is that these are actually TXB0108 but its pin-interface doesn't agree with your schematic.

Thank you for clarifying this point.

paul
 

MicroCoreLabs

Experienced Member
Joined
Feb 12, 2016
Messages
119
Question about the 74LS245 in the circuit, what is the 245 type you used? HC?



Where is the BOM located, please? I don't see it in GitHub. The schematic states 74LS245 but specifies 3.3VDC. Your web pages states "SMT buffer". The visible markings on the eBay listing are nondescript (or at least indecipherable by me); LX2458 doesn't seem to correspond to any TI part.

My best guess is that these are actually TXB0108 but its pin-interface doesn't agree with your schematic.

Thank you for clarifying this point.

paul


Hi,

The BOM is on GitHub here: PCB/PCB_FIILES/BOM.txt

The parts are the SN74LVT245BDBR which are 3.3V parts that are 5V tolerant. This part symbol is not in KiCAD, so I probably used whatever x245 parts that was available.

Are you going to start a similar project?

Thx
-Ted
 
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