Dr. Scott M. Baker has brought another classic Intel machine back from the brink, restoring a CPU-less Intel Prompt 80 trainer to working order — then going a couple of steps further by converting it into a Forth machine and adding speech synthesis capabilities.
“I bought a[n Intel] Prompt 80, without CPU board, from eBay,” Baker explains of the project. “Basically, it’s what many people would call a ‘trainer.’ Lots of trainers existed in the day to give people access to a microprocessor so they could type in and execute a program without having to design the hardware. It let you get up and running with a CPU, in this case the [Intel] 8080 CPU, quickly. This could be as both an educational tool for new programmers as well as a marketing tool for CPU companies, to rapidly get their products into the hands of potential developers and customers.”
Launched in 1976, the Intel Prompt 80 is a basic system by modern standards: a 2MHz Intel 8080 processor sits on a CPU board inside a housing with a 16-key hexadecimal keypad, eight function keys, and a nine-key input/output segment, and with just 3kB of ROM and 1kB of RAM as standard there’s not much room to move. There’s no video output, either: just an eight-digit LED display and 16 indicator LEDs — though you can connect the system other devices over parallel or serial port connections.
Of course, without a CPU board the trainer isn’t going to be doing anything much: it’s a largely-empty box, with a few keyswitches on the front, a seven-segment display, a handful of LEDs, a ZIF socket for a DIP-format EPROM, and a power connector. It hadn’t come from Intel that way, but the seller had decided to split the machine up for parts — and Baker demurred at paying the asking price to put the original Intel Single Computer 80/10 in the case. Instead, he found a cheaper and newer 80/10A — then, later, upgraded it still further to an 80/10B, which still features the required Intel 8080 processor but quadruples the RAM to 4kB and adds a multimodule expansion slot.
With the new CPU board installed and a repair to the power supply, Baker had restored the Intel Prompt 80 to fully working order — but that wasn’t enough. The next stage was to put the Forth programming language into ROM — “[it’s] my favorite vintage programming language,” Baker explains, “[and] having Forth on the Prompt 80 is fun as this gives us a high-level language we can program in via the serial port” — and, finally, give the machine a voice by installing a speech synthesis multimodule.
Initially, Baker used an Intel SBC 80/10A before switching to an 80/10B with four times the RAM. (📷: Dr. Scott M. Baker)
“The Prompt 80 is a really cool trainer,” Baker concludes. “It’s bigger and heavier than most single board computer trainers of the days (and it’s actually a two-board trainer). The use of a multibus board as the CPU board allows you to easily swap different boards in — we could easily use an 8085 board or an 8086 board albeit with a rewritten monitor if we wanted to. Having two sets of LED displays with one dedicated to viewing registers is a nice touch.”
The project is written up in full on Baker’s website.
