6502.org

Hi Everyone,

I am planning to build a copy of the first micro-based system on which I programmed - it was an Acorn System 1 at secondary school in the UK in 1979. Details here: http://speleotrove.com/acorn/index.html

I aim to be as faithful to the original design as possible and most of the parts can be obtained fairly easily (except, see below). I am at the parts gathering and design stage and am pondering a few things for which I'd appreciate your input and thoughts:

• * Although I am doing this for myself, is there any interest from others? If so I'll document the build, make it more repeatable (see below), and also publish any info that may be of use for others.
  * The INS8154 RAM/IO chip is hard to track down at a good price - I am being quoted around $35 each with a minimum order qty of 10 or 20 (where available). Looking at the spec sheet, I feel I could do a pin-compatible emulation using a microcontroller without too much trouble (although it would be useful to also have the real part to check timings etc.), but has anyone emulated this chip already (microcontroller or CPLD etc.) and can anyone suggest a good place to buy one. I am based in the UK but will be in the USA for two weeks in June 2015.
  * Any encouragement to go ahead and emulate the INS8154? Would this be useful to others (if it's not already been done)?
  * Easiest way to program the 74S571 PROMS or an EPROM (I have quite a few 27xx devices) - I have seen a few designs 'out there' for simple programmers based on Arduino and PIC Micros, but is there a 'go to' one in this field?
  * Original crystal frequency is 1.006MHz. Any ideas where to get one before I just go with a 1MHz part?
  * I'm tempted to just wire wrap the boards (2), but if there is sufficient interest that others may want to build a copy perhaps I'll lay out PCBs and see whether I can make them similar in size/shape to the original - perhaps even aiming for single sided boards so they can be a DIY etching job.

Hopefully I'll find some time in the near future to kick all this off.

Thanks in advance.

Hi linker3000 and welcome to 6502.org.

After looking at the documentation a bit, I wonder if a 6532 might be a suitable replacement? Like the INS8154, the 6532 has two eight bit ports and 128 bytes of RAM memory, though using a 6532 would require minor design changes;

(1) use the 6502 PHI2 and R/W signals on the 6532 instead of the NRDS and NWDS signals.
(2) the signal going to the M/IO pin on IC2 (the '8154) should be inverted and go to the RS pin on the 6532.
(3) the A0 and A1 address lines should be swapped on the 6532 to match the '8154 register addresses.

Of course, being "faithful to the original design" might rule out the use of the 6532.

BTW, there appears to be a few Asian sources for "new" INS8154 devices for around $15USD (landed), if that helps.

Not sure what you can do about the crystal frequency. I suspect that's particularly important for tape operation?

Good luck on your project.

Cheerful regards, Mike

Mike,

Thanks for the welcome and the feedback.

I noticed that a few broker-type searches reported reasonable stock levels in the Far East, but I haven't any responses to RFQs - and the search sites don't give away the names of the vendors they are listing. Can you suggest any reputable suppliers I can approach - I found a few general forum threads on purchasing but no specifics for the region.

Thanks for the info on replacing the 8154 - that would be plan C after an emulation attempt.

Crystal freq - um, yeah. Have to see what happens!

linker3000,

Here's one of the INS8154 listings from a vendor I've used before.

I enjoyed reading about and studying the Acorn System-1 design yesterday. Please keep us updated on your progress.

Regards, Mike

Thanks - it's the darndest thing that searching for INS8154 and variants on ebay.co.uk (as I have been) rather than .com doesn't find them!!

Funny, I've noticed the same thing. In the past I've found some items listed on ebay.uk that don't show up on the US site. Curious, yes, no?

Thanks to you and your post, I've probably spent four or five hours total now looking at Acorn System-1 schematics and documentation. You should be ashamed of yourself (grin). Seriously, it's very interesting (to me) to see how so many of these early systems are so similar in design. After studying designs like the KIM-1, the Elektor Junior, and now the Acorn System-1, I'm reminded how components, especially memory, were so incredibly expensive during those early years and how that may have affected system design.

BTW, I found a picture of Sophie Wilson's System-1 prototype which doesn't include the tape circuitry or the 1K RAM chips. This is a very nice looking prototype.

Cheers, Mike

After looking over the other documents (Schematic and technical manual parts list) on the site you referenced, I believe the crystal is a standard 1 MHz part, not 1.006 MHz.

The only reference I saw to 1.006 was in the photo. It's possible the 6 represents the decimal shift value, i.e., 1.00 x 10^6 Hz.

Good luck with your project!

Daryl

The photo doesn't show 1.006 though, it's 1.008 (it's just that the ink has come off on the right side)

On the other hand the image at this link clearly shows 1.000 MHz.

-Tor

Thanks to everyone for the feedback and extra pairs of eyes. You're all correct about the crystal - the one in the original photo is 1.008MHz but the one in the wikipedia photo and original parts list is 1MHz so I'll be going for that.

I'll order an INS8154N from UT Source - any opinions on % likelihood it's a genuine part?!

If/When I get my system up and working I might still try to emulate the chip using a microcontroller as a 'fun' side exercise.

I'm gathering parts now - just need to decide on how to make up the keyboard and whether to do wire wrap or layout PCBs.

I have found the Nat Semi doc on how to program the bipolar TTL PROMs - it doesn't look like it would be too difficult to rig up something to either do it manually, or under the control of, say, an Arduino, but, again, if anyone has already invented this wheel do let me know otherwise it will be another side project!

utsource is one of the more reliable ones as far as ebay stores are concerned. Several members here have purchased old parts there and I haven't heard any negative stories. No guarantees though.

-Tor

Thanks again for the feedback. Ordering a pair of 8154s now.

Here's another part sorted - had this knocking around in my 'LED Displays' drawer for about 20 years (as you do!) - it's marked as an "Antex SK-2-151" and it is pin equivalent to the original NSA1198.

LED calculator displays were suitable for when you need something tiny. Here's one with four digits, end-stackable for 8, 12, 16, etc. (from the displays page of my 6502 primer:



Avago Technologies has some very nice similarly-sized sets of four-character serially fed LED displays in 5x7 dot matrix at http://www.avagotech.com/pages/en/led_d ... hcms-2963/, but they're not cheap!

Hey linker', do you have a link to that document, please?

Mike

By strange coincidence I have a board with a pair of those displays that I'm going to desolder.

They are very expensive. Around £30 each in the UK in small quantities.

Document attached. P5-1 for voltages and timings.