Nice proof of concept. Seems pretty decent for a late 70's computer.


Do you have a time machine or is this something that was designed in the '70s.

I planned to build some sort of computer, in the late 1970's but never had the money or access to parts or the time. Now
I got the time and the internet for information. Now and then I could get to a city, with a RADIO SHACK and buy the $5 grab bag

https://radioshackcatalogs.com/flipbook ... talog.html
In the early 1980's I got a Z80 /S100 kit, but the homade power supply toasted it, on a bad day.

I did get to use a PDP-8 once . but never could buy a used PDP, so it was too collect parts and build my own
computer using 2901's. With 2901's a 20 bit computer seemed like possible project, 5 slices wide
rather than 4 for a 16 bit computer.
After getting internet faster than 9600 baud, Home brew designs like MAGIC got me interested in them again.
I was delayed about 10 years building a nice audio system, then I got Altera FPGA development card and have been
prototyping with ttl logic, on them on the last few years.
http://www.homebrewcpu.com/
For audio https://www.enjoythemusic.com/magazine/sound_practices/ was nice place to start.
With covid, parts have dried up, so I am using 16v8's replace things like 22v10's that replaced
82s100's from the late 70's.
Ben.

(It's a shame to lose a drafted post, but welcome back to the days of save early and save often...)

At 300 baud it will take a while, time for a new thread.

Ball park schematics and bus are done, for the version with decimal operations. Needs the use of half power PAL's
that came out around 1983. Excess 3 decimal operations and Dubble Dabble adjustments, are new from 1976.
1 uS memory cycle ~1976, .65 uS memory cycle 1983.
Ben.

Adapted some older decimal floating point code, but needed a 2 more registers for the mult/divide inner loop. so I added a exchange instruction
like on the z80. It works but made the design messy. Over the weekend I removed the +- 8 bit constant, freeing up a bit, so now I have up to 16 registers
rather than 8 to work with. No need to have the exchange operation now. Only 12 registers fit, on the fpga how ever. I am happy with this design, and ready to clean up the software, this fall.
Ben.

Final change, BCPL freindly as I switched from little endian to big endian.
Ben.

Are you sure? Although really, it makes no difference - the existing compiler can output code for little or big endian, but little endian is the default. (And having written a cintcode interpreter/vm in a little endian system, it all seemed to "just work" in that department)

-Gordon

Is this a 16 bit or 32 bit BCPL?

My implementation is a 32-bit one - running on a hybrid 8/ bit CPU with an 8-bit memory bus (ie. the 65c816). The last BCPL system I used was a 16-bit one running on an 8 bit cpu (6502).

(and I'm referring to Martin Richards Compiler - I suspect there are others out there but I've no idea how they handle endian)

-Gordon

I will be using "Robert Nordier"'s version of BCPL. (icint.c) and Pelles C compiler under windows XYZ to get BCPL working under windows.
I will later change the case statements to if statements and then translate that for my machine.
Ben.

Made a few minor changes in the hardware, and now I get routing bugs. My front panel display program is now shifting left when it is programmed to shift right.
I am quickely running out midnight oil here, Ben.

Sounds like a direction bit is flipped.

Could be a new "feature".

I could not solve the problem, so I had to roll back to a earlier version that used less block ram.
I am leaving the instruction set as is. and plan to work on external I/O. I planing a 16 bit hexadecimal front panel
rather than a binary one, and a new setup for serial and SD cards. Now if I could only find 14 segment NIXIE TUBES
rather than the common 7 segment led's.
Ben.

ин-14 nixie tubes? But these are not segmented.
Or 14 segmented vacuum fluorescent display, somehow in nixie red?
Maybe from some unrepairable chess computer, last place I saw anything like that...
Go big with orange/red EL ropelights.