Classic computing fanatic Michael Wessel has turned a Raspberry Pi Pico into static RAM (SRAM) emulator and SD card storage interface for the Multitech Micro-Professor MPF-1B — bringing with it some severe quality-of-life bonuses.
“Give your Micro-Professor MPF-1B (and different machines) a flexible SD card interface — no extra cassettes,” Wessel writes of his creation. “Emulate 2kBs of 6116 SRAM with a Raspberry Pi Pico and use an SD card for storing and loading full reminiscence dumps! Its first use case is to emulate the U8 2kB system RAM from 0x1800 to 0x1FFF on the Micro-Professor MPF-1B. You will not want the cassette interface any longer — simply use the SD card.”
Launched in 1981 by Multitech, which nonetheless makes computer systems immediately below the extra recognizable title Acer, the Micro-Professor MPF-I used to be a Zilog Z80-based single-board pc which aimed to show the core ideas of programming for the chip. The machine’s output was proven on a six-digit seven-segment show, whereas packages could possibly be saved — slowly — to cassette tape.
It is this gradual storage medium Wessel’s creation replaces, bypassing the machine’s personal storage system so as to load and save on to RAM near-instantaneously — through the use of a Raspberry Pi Pico’s RP2040 microcontroller to emulate the machine’s authentic 2kB RAM chip.
Getting the machine up and operating proved a problem — not least of all because of a scarcity of GPIO pins. (📷: Michael Wessel)
“The primary problem was a scarcity of GPIO [General-Purpose Input/Output] pins on the Pico,” Wessel writes of the venture. “The 6116 [SRAM chip demands] a whooping eight bits of information IO, 11 bits for the tackle bus, plus OE [Output Enable] and WE [Write Enable] — 21 GPIOs of the max. 26 that the Pico presents.”
Provided that Wessel additionally wished to supply a person interface with an OLED show, and storage on an SD card slot, further GPIO pins have been required — which have been offered by multiplexing the tackle bus utilizing two 74LS373 eight-bit latches. “The 2 latches are mainly simply used for his or her tri-state/Excessive-Z capacity,” Wessel explains, “I’m not even utilizing them as latches.”
The machine offers the power to load and save full 2kB reminiscence dumps near-instantaneously from microSD storage. (📷: Michael Wessel)
This is not the primary machine Wessel has constructed from a Raspberry Pi Pico so as to provide quality-of-life enhancements for classic computer systems. Again in September he unveiled an add-on for the Busch 2090 Microtronic Pc System, the PicoRAM 2090, which aimed to work across the machine’s painfully gradual 14-baud cassette interface with microSD storage.
The ultimate machine works completely on an actual Multitech Micro-Professor MPF-1B — even pulling its energy from the host system immediately — and, Wessel notes, also needs to work “with different 6116-based computer systems.” Extra info on the venture is accessible on Wessel’s Hackaday.io web page.