A Raspberry Pi Pico (RP2040)-based 6161 SRAM Emulator, SD Card Interface, and Multi-Expansion for the Multitech Microprofessor MPF-1B and MPF-1P SBCs (Single Board Computers).
Demo videos:
-
Microprofessor MPF-1P Z80 PicoRAM 6116 and MPF-1P Printer - The Towers of Hanoi
-
Microprofessor MPF-1P Z80 Assembly Programming with PicoRAM 6116 - The Towers of Hanoi
-
Microprofessor MPG-1(B) Z80 Assembly Programming with PicoRAM 6116 - The Towers of Hanoi
The development logs are on Hackaday.
This project is a follow-up to PicoRAM 2090 for the Busch Microtronic Computer System; also see the development logs on Hackaday.
Hackster covered the PicoRAM 6116.
I also archived the PDF of the Hackster article.
PicoRAM 6116 is the ultimate expansion for the vintage Microprofessor SBCs.
Features:
-
SD card interface: loading and saving of programs (full SRAM memory dumps) and easy file exchange with the PC (FAT32 filesystem). ASCII HEX format, additionally supporting comments and target addresses.
-
Plugs into the U8 6116 socket on the MPF-1B (address range
0x1800 - 0x1FFF) or the U5 6116 socket on the MPF-1P (address range0xF800 - 0xFFFF). -
Comfortable UI: 5 buttons and OLED display.
-
4 user memory banks: the currently active memory bank can selected over the UI; each bank hosts a full 6116 SRAM.
-
Autoload feature: the
6116.INIfile is loaded during startup and allows the specification of an autoload program for each of the 4 memory banks. -
Easy build & installation: PicoRAM 6116 uses pre-assembled off-the-shelf modules and through-hole components only, and no (destructive) modifications to the Microprofessor are required.
The JP1 Jumper should be in the right position:
The current version is PCB Rev. 4. This PCB hosts an extra single pin connector (J1). Connect J1 to the Microprofessor's WAIT on the expansion header (PIN 37):
If you don't use the J1 to WAIT connection, you will need to hold the Microprofessor in RESET while operating PicoRAM - see the Rev. 3 Demo Video. However, this is no longer required with Rev. 4 (the current version from this repository) - as shown in the Rev. 4 demo video). This video shows the MPF-1P, but it also applies to the MPF-1B.
PicoRAM needs a FAT32-formatted (max 32 GB) Micro SD Card. Copy the
appropriate 6116.INI file to it, and get the correct demo programs
for your machine (MPF-1B or MPF-1P). Unzip everything to the root
directory; sub-directories are not supported. See this
directory.
PicoRAM 6116 is usally powered over the 6116 SRAM socket. Make sure that the POWER button is pushed down, and that the SEL VCC (Power Source) is set to 6116 VCC. External power supply is possible as well, using the 5V Center Positive Barrel Jack. However, this should not be required. The LEDs 6116 VCC and EXT VCC light up indicating which power sources are available (i.e., if both EXT VCC and 6116 VCC light up, it means that you have power over the 6116 Socket from the Microprofessors, as well as VCC from the external power supply). Then, use the SEL VCC switch to determine the utilized power source (either external or internal). If you have an external power source connected, but EXT VCC stays dark, then you probably have the wrong polarity.
The 5 UI buttons are using the Pico's analog input. Unfortunately, the
analog levels turned out to be very noisy and also vary from machine
to machine. So it might be necessary for you to "tune" these
analog threshold levels to match your machine. The 6116.INI file
supports this. The init file looks as follows for the MPF-1B
(not that UNIX EOL is required! a single newline / 0x0A character):
MPF-1B
D00
C00
900
700
300
100
CLOCK.MPF
DICE2.MPF
COUNTER2.MPF
EGGTIME.MPF
0
The file lists, in this order:
- the name of the machine
- the analog threshold for the CANCEL buttons (used during YES/NO dialogues)
- the 2nd analog threshold for the CANCEL buttons (toplevel buttons)
- the analog threshold for the OK button
- the analog threshold for the NEXT/PREV button
- the analog threshold for the UP button
- the analog threshold for the DOWN button
- 4 lines for the 4 autoload programs for banks 0 to 3 - use an empty line for no program
- 0 or 1; 0 for normal operation, and 1 is used to enter a debugging program which can be used to determine the above analog threshold for the buttons above.
Note that the default init files for the MPF-1B and MPF-1P are supplied, and that the analog thresholds differ. They were determined with the author's machines, and might not work for your machine.
The Pico emulates the 6116 SRAM of the Microprofessor:
The Pico is overclocked to 250 Mhz to make this possible; this is completely in the safe range and does not affect the longevity of the RP2040 in any negative way.
Due to a lack of GPIOs on the Pico, I used two 74LS373 transparent
octal latches to multiplex the 11-bit address bus. The 11-bit address
is read in two batches of 6 and 5 bits, using the SEL1 and SEL2
signals from the Pico to OE (Output Enable) the first resp. second
latch. The latches are merely used for their tri-state capabilities.
Unlike my previous design, PicoRAM 2090, this design does not utilize any voltage level converters. It turns out that the Pico (RP2040) is really pretty much 5V-tolerant; also see this article from Hackaday and the Hackaday coverage of PicoRAM 2090.
More details about the making of the project, and technical notes / development log can be found on the Hackaday project page.
Schematics:
The current version is Rev. 4, December 2023.
There is also a Bill of Material (BOM).
See here.
The current version is 1.1, December 2023 and the .uf2 image can be
found here.
See here.
-
Harry Fairhead for his execellent book!
-
Hans Hübner (aka Pengo) for motivating me to abandon the BluePill, ATmegas and Arduinos, and for helping to get started and troubleshooting!
-
The authors of the libraries that I am using:
-
Carl J Kugler III carlk3: https://github.com/carlk3/no-OS-FatFS-SD-SPI-RPi-Pico
-
Raspberry Pi Foundation for the
ssd1306_i2c.cdemo.
-