Using an AVR to emulate obsolete part.

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Has anyone had experience replacing and obsolete part with a micro controller?

Specifically I want to emulate a Texas Instruments TMS5501. I have a few old Cromemco S-100 computer boards that use this part. It seems to be made of unobtanium. Although some web sources say they have them, they never reply to inquiries. Yes, I know I won't be a drop in replacement. I plan on making a carrier for it.

Any input would be appreciated.

Roger

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The TMS5501 is not a microcontroller. It's a 8080 companion i/o interface chip which has timers, UART, parallel port and interrupt controller.

Your best option is to throw away all this crap.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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Quote:

is not a microcontroller

I'm not sure I can spot the place where OP claimed otherwise? But for sure you can use an MCU to replace an I/O expander or a group of TTL gates or pretty much anything that is less complex than the MCU itself (assuming you can wiggle the wires quickly enough etc. etc.)

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Without finding a datasheet for that thing, a quick ballpark estimate:

What is the clock frequency of that thing? Maybe 1 MHz? If you would use a 16 MHz AVR this gives you 16 AVR instructions per one target clock cycle. Are you sure you can emulate every behavior with that amount of instructions? I doubt it.

Stealing Proteus doesn't make you an engineer.

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An XMOS chip wouldn't have any problems with that:

http://www.xmos.com/

Leon Heller G1HSM

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clawson wrote:

I'm not sure I can spot the place where OP claimed otherwise?

Yes, overlooked that.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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ArnoldB wrote:
Without finding a datasheet for that thing,...

See the link I provided above.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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It depends on exactly what you want to achieve. I would suggest a CPLD if you want to make a drop in replacement. Something like a XC95108 as it is 5v. Anything later is most likely 3V. Leon's XMOS suggestion would also be worth investigating, but it is 3V. The bus interface presents the biggest problem in using an AVR for the emulation. Using a larger microcontroller you will be able to emulate the whole cpu and most of the peripherals - I squeezed a Z80 emulator running CP/M with disk drives emulated on a micro SD card into a TI/luminary LM3S6965 chip without much trouble. Using this, you have the choice of either emulating the peripheral in software or trapping the functions that access it and doing whatever is needed.

The MAME and MESS projects are a good place to look for emulations.

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MBedder wrote

Quote:
Your best option is to throw away all this crap.
This is heresy. My old S-100 computers have been with me for a long time and have contributed greatly to my comfort in my approaching senior years. I couldn't throw out an old friend.

My thought was it would be a simple task for the AVR to manage all the peripherals in the 5501 and use an ISR to move data in and out.

ArnoldB had the most "damaging" feedback for my plans. The ISR would not be fast enough to meet the speed requirement. The S-100 CPU would be running at 4MHZ. Bummer. The CPLD would work, but I don't know enough about them and to be honest I have no desire to learn a new skill in this direction. I would rather spend that time shooting clay targets. Considering the cost of a XC95108, I could use several AVR devices and distribute the tasks. I guess I will set down and see how fast I can actually make the ISR. What I did not want to do was use a wait signal but this is an option.

Thank you all for your input and advice.

Roger

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polecat,

You said s-100 computer, is it those with s-100 bus back in the days of the altair & CP/M OS?

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Yes. Cromemco was very fond of using the TMS5501 for it's serial ports.

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Wow! people still using those machine ? I wanted to build one back then but didn't have money for it, too young :); but I had access to play with Z80 CP/M machines with a 5" floppy disk (Superbrain, TRS-80). I did even wrote my own Z80 assembler/disassembler. CM/P has an 8080 assembler but I wanted to use Z80 instruction set. It was fun, I loved it. I understand you're attachment to it. I had nostalgia of that era myself from time to time.

I believe you could emulate it with a micro. An AVR can have it's I/O running at 8MHz. With a bit of software, it would do nicely.

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The TI-810 dot matrix printer had a 5510 40-pin dip in it.

Maybe you can get an old working printer.

A bit info on the chip here
http://cbm.bobnj.com/articles/By...

Is this the board you have ?
http://s100computers.com/Hardwar...

http://s100computers.com/Hardwar...

/Bingo

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If you're happy with wait states, you could add a flip/flop to assert wait when the chip/board is selected, have the AVR interrupted and toggle an AVR port pin to release the wait when it has done ts job. You'll also need some latches so you get a tristate data bus

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Kartman wrote:

Quote:
You'll also need some latches so you get a tristate data bus

OH RATS! I forgot about the tristate outputs. All things considered, it looks like it's time to file this project away.

Bingo600 wrote:

Quote:
The TI-810 dot matrix printer had a 5510 40-pin dip in it.
I have a couple of those and several rebuilt printheads. Maybe I can wait for one on ebay. I wouldn't be attached to one I just got.

A great deal of my problem here is, I'm not a rational person when it comes to my antiques.
Looks like my time might be better spent on building a clay target thrower using an AVR.

Thank you everyone for your input. I will move on to other things and put this idea to bed

Roger

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You might also check out...

[usrl=http://s100computers.com/]S100 Computers[/url] - has a nice collection of website pointers, too.

The Vintage Computer And Gaming Marketplace

Stu

PS: I live in Fort Collins

Engineering seems to boil down to: Cheap. Fast. Good. Choose two. Sometimes choose only one.

Newbie? Be sure to read the thread Newbie? Start here!

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polecat wrote:
Looks like my time might be better spent on building a clay target thrower using an AVR.
Or, if you have a dog, and automatic ball thrower! :lol:

Stu

Engineering seems to boil down to: Cheap. Fast. Good. Choose two. Sometimes choose only one.

Newbie? Be sure to read the thread Newbie? Start here!