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Old 5th Apr 2023, 1:02 am   #1
River25
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Default My Home Built SC/MP II SBC

Hi,

I like to design, build and program small SBC (single board computer) using the old, original 8-bit CPUs of the 70s. One CPU I have mucked about with for many years is the SC/MP. It is both annoying and rewarding when you get this old, cumbersome CPU to do the things you want. I had an old ceramic SC/MP II CPU about, with "suspect?" written on it, so I had to see if it really was suspect or not and tested it via a simple breadboard set-up and it worked. I then decided to solder up a veroboard version and make my SC/MP II SBC come to life.

This system was built mainly for fun, as I had no real purpose for it, except to build a SC/MP SBC. Anyway, I now have a purpose for it, and it will be running a 6264B RTC, a couple of pushbutton switches, a bunch of relays and a 16x2 backlit LCD display. This system will be used to switch between input components (ie Phono deck, cassette deck, R2R unit, CD player, etc) between two old amplifiers, and also do the relevant speaker switching.

I have buffered the SC/MP address, data and control signals, and by using a 74HC154, I have split the SC/MP memory range into the same 4k page limit of the CPU. It currently runs with 4K EPROM (2732) at page 0, with another 4K EPROM capability at page 1. I have 4k of RAM (2 x 6116) at page 3. The other page selects, except the final 2 pages are available for expansion. The second last page is for the 8251 serial communications device, and the final page is for the 8255 parallel interface. While the SBC was built to be fairly generic, I may have to add a few things here and there to get what I want for my stereo switching functionality. The SC/MP SBC works fine. The serial comms work as to does the 8255 parallel ports. I am at the stage of designing software for it, by pre-testing, using my home built 8085 development system. One of the things I need to get sorted on the SC/MP SBC is my Intel hex downloader so I can do changes and download on-the-fly to test the SC/MP ports etc.

I hope I got the attachment bit sorted here, and you can see my grubby little SC/MP II SBC. She isn't very pretty, but she is a lot of fun and works brilliantly well.

river
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Old 5th Apr 2023, 9:11 am   #2
SiriusHardware
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Default Re: My Home Built SC/MP II SBC

Oh, lovely, a discrete 8-bit microprocessor project entirely built on stripboard / veroboard. That's very hardcore. Thanks for showing us that, and welcome to the forum.
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Old 5th Apr 2023, 7:40 pm   #3
coolsnaz2
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Default Re: My Home Built SC/MP II SBC

Great to see another SC/MP, not sure if you have seen the Hex file downloader I have developed for the MK14,

https://www.vintage-radio.net/forum/...d.php?t=186247

It would be interesting to see if it would work with your system, or maybe you already have a hex downloader.
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Old 5th Apr 2023, 8:39 pm   #4
Realtime
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Default Re: My Home Built SC/MP II SBC

Excellent stuff!. Reminds me of the first breadboard uProcessors that I built 40-odd years ago (on pad board I think rather than vero board). The first was a 6802 with 2K RAM and 4K EPROM and latches for the parallel GPIO - still have the core chips from that. I then built a 6502 based sensor board for a micro-mouse competition with some friends in the mid 80's and later moved on to the the 8051, probably my favorite uP family in truth. I'm happy to have discovered the 8060 in that last couple of years and as you say, despite the limitations and sometimes frustrations of its instruction set, it's very satisfying to get it running.

Lovely white ceramic processor by the way . I notice you have a crystal and a DIL oscillator on board. One's for the processor - what's the other one for?

How will you be controlling the LCD display? Bit bang'd using the 8255?
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Old 5th Apr 2023, 9:42 pm   #5
River25
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Default Re: My Home Built SC/MP II SBC

Hi,

Quote:
Originally Posted by coolsnaz2 View Post
Great to see another SC/MP, not sure if you have seen the Hex file downloader I have developed for the MK14,

https://www.vintage-radio.net/forum/...d.php?t=186247

It would be interesting to see if it would work with your system, or maybe you already have a hex downloader.
I will go check it out. No point re-inventing the wheel if you have already done it. I will let you know how I go.

river
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Old 5th Apr 2023, 10:03 pm   #6
River25
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Default Re: My Home Built SC/MP II SBC

Hi,

Quote:
Originally Posted by Realtime View Post
Excellent stuff!.
Lovely white ceramic processor by the way . I notice you have a crystal and a DIL oscillator on board. One's for the processor - what's the other one for?

How will you be controlling the LCD display? Bit bang'd using the 8255?
Yes, one crystal is for the processor and the other one is for the serial communications to get the baud rate clock generated for the 8251 device. Whenever possible, I try run crystal circuits on my processors and circuits.

I am currently testing the LCD display on my 8085 development system by hanging it straight off the data bus and going the full 8-bit wide rather than 4 bits. I control the command sequences to the LCD by calling a simple software timing loop, as the LCD "busy" flag doesn't seem to always want to play nicely. This works fine as the lowest timing resolution the LCD will display (for my purposes) would be seconds, but most likely minutes, so the small milliseconds long delays between command updates won't be an issue. On the SC/MP SBC the "spare" 4732 slot, at page 1, can be used to connect the LCD display. I have a 24-pin IC header so I can attach the LCD via that, without having to change or modify anything on the SC/MP SBC. This frees up the 8255 which allows me to put in my pushbuttons and relays without requiring another device.

I need to add the RTC chip, and I will probably do something similar as per the LCD display. The SC/MP SBC has 2 x 6116 (2kx8) RAM chips and I will not be needing that much RAM, so I can use another 24-pin IC header and replace a RAM chip with the RTC chip. Again, this requires no modification to the original SC/MP SBC, which is good.

Will I use SC/MP interrupts for my RTC and/or user-pushbutton-input? Maybe I will. Not sure yet, as I am certain some of you old "SC/MP heads" know the weird way the SC/MP handles it's interrupts, and the poor little thing really hasn't got enough spare P-registers to sacrifice one to sit and wait for something to happen. But hey, it's another challenge and something I will play around with as I continue developing it.

If people here are interested, I will do a progress report on my development of this system, which includes the preceeding 8085 work to establish base line code, followed by the SC/MP code and set up of the same thing.

river
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Old 6th Apr 2023, 3:41 am   #7
River25
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Default Re: My Home Built SC/MP II SBC

Hi,

Quote:
Originally Posted by River25 View Post
Hi,

Quote:
Originally Posted by coolsnaz2 View Post
Great to see another SC/MP, not sure if you have seen the Hex file downloader I have developed for the MK14,

https://www.vintage-radio.net/forum/...d.php?t=186247

It would be interesting to see if it would work with your system, or maybe you already have a hex downloader.
I will go check it out. No point re-inventing the wheel if you have already done it. I will let you know how I go.

river
I went hunting through that thread and it appears the zipped code in post #168 is the current version to use?

river
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Old 6th Apr 2023, 7:58 am   #8
SiriusHardware
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Default Re: My Home Built SC/MP II SBC

Coolsnaz2's code was very skillfully written to fit into a specific space in the existing 512 byte PROM of the MK14 and as such uses a simplified protocol with an-off machine companion program, script or server providing the translation from Intel Hex to the intermediate protocol.

I notice that River25's projects all include a MAX232 RS232-TTL level converter and some sort of UART so his preferred method seems to be to have the Intel Hex download and translation to raw hex implemented on the system itself, which he is easily able to do because, unlike on the MK14, he has plenty of spare EPROM space in which to place fully functional RS232 serial Intel Hex download code.
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Old 6th Apr 2023, 1:15 pm   #9
River25
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Default Re: My Home Built SC/MP II SBC

Hi,

Quote:
Originally Posted by SiriusHardware View Post
Coolsnaz2's code was very skillfully written to fit into a specific space in the existing 512 byte PROM of the MK14 and as such uses a simplified protocol with an-off machine companion program, script or server providing the translation from Intel Hex to the intermediate protocol.

I notice that River25's projects all include a MAX232 RS232-TTL level converter and some sort of UART so his preferred method seems to be to have the Intel Hex download and translation to raw hex implemented on the system itself, which he is easily able to do because, unlike on the MK14, he has plenty of spare EPROM space in which to place fully functional RS232 serial Intel Hex download code.
Ahhh, okay... that explains it.

Yes, I have quite a number of spare parts, including CPU, peripheral chips, memory chips etc, across a range of various CPU types and bus/signals and all that. So, I have the luxury of being able to put together the systems with UARTS and RS232 converters and have the capacity to write the translation on the target device. I am currently debugging my SC/MP Intel Hex file code. Are you interested in it when I have it operational?

river
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Old 6th Apr 2023, 1:43 pm   #10
SiriusHardware
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Default Re: My Home Built SC/MP II SBC

We are always interested in anything SC/MP related whether it is a code project, a hardware project, or a combination of the two, and would prefer it to be available to anyone potentially interested in it (that is, posted here on the forum for anyone to be able to look at) but that is entirely up to you of course.
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Old 6th Apr 2023, 9:46 pm   #11
River25
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Default Re: My Home Built SC/MP II SBC

Hi,

Quote:
Originally Posted by SiriusHardware View Post
We are always interested in anything SC/MP related whether it is a code project, a hardware project, or a combination of the two, and would prefer it to be available to anyone potentially interested in it (that is, posted here on the forum for anyone to be able to look at) but that is entirely up to you of course.
No problems and agree. It is always good to find other resources of similar work so you can see what others are doing, learn new things and impart old knowledge.

I will clean up my circuit diagrams and will post them up so anyone here can build their own SC/MP II SBC or equivalent. More so when I get my Intel Hex file download working, as this will enable the user to load up any software quickly into the system to play about and do whatever they wish.

river
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Old 6th Apr 2023, 10:54 pm   #12
Michael Haardt
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Default Re: My Home Built SC/MP II SBC

An Intel HEX file loader would be very interesting, especially one that is fast enough for coupling it to the software UART functions typically found on SC/MP systems. I did that for the MCS-48 and had much fun how easy it was to load software.
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Old 12th Apr 2023, 6:26 pm   #13
Slothie
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Default Re: My Home Built SC/MP II SBC

Lovely to see another design. I'm a particular fan of hand-wired computers made on bare matrix board or veroboard, I saw a lot of ex-computer boards done this way in scrap computer parts places in the late 70's early 80s (anyone remember Display Electronics and that place in Maldon?) and a lot were wired in this fashion, sometimes with wire wrap and sometimes more primative methods. My father and I salvaaged a lot of parts from those boards....
Anyhoo back to the subject, its nice to see someone exploring the possibilities with contemporary ICs ewithout the usual tight budget constraint of the time that usually applied to these computers.
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Old 12th Apr 2023, 9:40 pm   #14
River25
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Default Re: My Home Built SC/MP II SBC

Hi,

Quote:
Originally Posted by Slothie View Post
Lovely to see another design. I'm a particular fan of hand-wired computers made on bare matrix board or veroboard, I saw a lot of ex-computer boards done this way in scrap computer parts places in the late 70's early 80s (anyone remember Display Electronics and that place in Maldon?) and a lot were wired in this fashion, sometimes with wire wrap and sometimes more primative methods. My father and I salvaaged a lot of parts from those boards....
Anyhoo back to the subject, its nice to see someone exploring the possibilities with contemporary ICs ewithout the usual tight budget constraint of the time that usually applied to these computers.
Yes, same here. It was intended to be a small fun project, but I got into it and made it a tad bigger than what I initially had in mind, which is fine, as it means the SC/MP system is buffered and fully expandable if extra components or functions are required.

I am also doing a solder-veroboard SBC, fully buffered so it can be expanded, for the Signetics 2650 CPU. I have completed the cct diagrams and have got all the chip sockets in place, with the relevant tracks cuts. It's just a matter of me spending some time to commence soldering it up, and then writing some form of monitor/debug code for it.

While that is happening I got to finish my SC/MP hex-file downloader, which is just about ready to run. And there is my 8755/2708/2704 EPROM burner running on an SDK-85 which I have done the cct diagrams and now got all the connectors and stuff, so I need to get that sorted and the software written. My cct design for a 6502 SBC is completed and this will be a wire-wrap job is ready to commence. Crikey... I got too much stuff going on and I am really best at single threaded applications. My multitasking is not very good. :P
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