Developer and classic computing fanatic Chris Burrows has been engaged on a retro-themed microcomputer constructed round a Signetics 2650 eight-bit processor — and a Raspberry Pi RP2350B-powered Olimex Pico2-XL microcontroller board to face in for each different required element.
“The [Raspberry Pi] RP2350 generates the 1MHz clock and the [Signetics] 2650 (an eight-bit MCU [Microcontroller Unit] from the Seventies) executes the code,” Burrows explains. “The Signetics Monitor ROM, Pipbug (or different ROM code) and the person’s software are loaded into RAM on the RP2350 which then companies the OPREQ alerts from the 2650.”
The Signetics 2650 rides once more, driving a sport of Othello on a brand new minimalist microcomputer design. (📷: Chris Burrows)
The Signetics 2650 was launched in 1975 as a single-chip processor designed to compete with multi-chip minicomputers of the period — with a design led by IBM’s John Kessler and primarily based on the corporate’s IBM 1130 minicomputer of ten years’ earlier. Not like the IBM 1130, although, the S2650 is an eight-bit chip, with a for-the-time excessive clock pace of 1.25MHz because of a low-power NMOS course of node. Regardless of being extra highly effective than Intel’s rival 4004 and 8008, the chip was not an enormous success — partially because of that very want to compete with minicomputers, which noticed it implementing options that had been merely pointless for microcomputers whereas lacking others.
Regardless of this, the chip nonetheless has its followers — together with Burrows, who has constructed a useful system round an authentic S2650 dubbed the S2650 IcePi. Except for the processor itself, there’s just one different main element concerned: the Olimex Pixo2-XL and its RP2450B microcontroller, which acts as every part from clock supply to ROM.
“With the ability to entry as much as 48 GPIO [General-Purpose Input/Output] pins got here in very helpful,” Burrows says of the undertaking. “There are two USB/RS232 adapter boards on this prototype. One communicates immediately with the 2650 SENSE and FLAG serial IO working at 4800 Baud. The second USB/RS232 adapter connects to RX/TX on the RP2350 to speak through the Astrobe terminal. The alternatives for tracing and debugging in real-time are limitless as all the information and deal with site visitors to/from the 2650 is intercepted by S2650 IcePi. This got here in very helpful throughout improvement.”
The undertaking is documented on the Astrobe discussion board, together with partial supply code.