WD1771 Board

UNICOMP

Version 3.00

A modular 8-bit Computer able to recreate (nearly) every microcomputer of the mid 70s to early 80s in Hardware without FPGAs (although an FPGA can be added). Can also be used as a teaching tool for:

• VHDL or Verilog
• C
• RTOS (STM32F401 runs ChibiOS. Link: https://www.chibios.org)
• Python
• bash and linux in general (Olimex board runs linux with fbterm and tmux)
• Harwaredesign
• Timing of CPUs
• maybe Assembler
• SPI and I2C Interfaces
• CPLDs and FPGAs

It is different from other designs because of these points:

• it uses a 3.3V only Bus,
• it uses fast RAM for 16 chipselect outputs with single address resolution over the whole 1MB range,
• it uses one SRAM for RAM and ROM replacement (can be write writeprotected) with 1MB,
• it uses a clock generator chip (DS1085) - no more crystals to change,
• it is configureable via STM32 (RAM and ROM content, Clock frequency, chip select lines),
• it can program the CPLDs (only XC9572 and XC9536 tested) from the STM32, no external programmer needed.
• Board size is 100mm x 100mm - no backplane (like the PC/104 standard. Link: https://en.wikipedia.org/wiki/PC/104).
• and maybe most convenient: it can change RAM and ROM content on the fly without crashing the CPU. For example starting the Apple I, going into Basic and uploading the program in about half a second is really nice.

Unicomp plus Logic Analyzer:

Unicomp modules

• USB-Serial board:

  • a simple board with an universal 4x USB to UART module from ebay (FT4232).

• CPU board:

  • can be any 8-bit CPU (6502, 6802, 6809, 68008, 6803, 8051,...)
  • a CPLD (XC9572) for clock generation and glue logic

• Multi Serial boaŕd:

  • suggested chip select #0
  • can be used with the following serial interface chips: MC6850, MOS6551, MOS6552 or pin compatible

• Multi Parallel boaŕd:

  • suggested chip select #1
  • can be used with the following parallel interface chips: MC6820, MC6821, MOS6520, MOS6521, MOS6522, MOS6526, MOS8520, MOS6532 in the first slot
  • the first slot can additionally mimic a MOS6530
  • the second slot can accommodate a MOS6522 or pin compatible

• RAMROM board:

  • chip select fixed at #15 (for chipselect RAM or ROM) and #14 for Write Disable (High for ROM),
  • 1M of SRAM plus an extra 16-bit RAM for address decoding,
  • a STM32F401 'blackpill' board to fill the SRAMs with data over USB,
  • USB shell on the STM32 to change ROM content on the fly,
  • also configures the Address Range of all peripheral modules,
  • acts as a XSVF Player to program the CPLDs

• Prototype board:

  • empty board for prototyping
  • no CPLD

• MAX-II (EPM240) board:

  • CPLD plus Buffers

• self made module:

  • chip select can be any non-used line in the Range from 0 to 13.
  • size is 100mm x 100mm
  • there is the prototype board in the repository for the position of the connectors and also the labels (pinout)

Configuration RAM

The configuration is done with 1Mx16 fast ram on the RAMROM board. It is configured from the STM32F401. The cs = 15 is for writing the main RAM, cs = 14 is the Write Disable. The rest is free.

Working Recreations of old computers (tested again with Unicomp3)

python helper scripts

• UC3_upload.py: multi-function script. up- or download RAM Content, write or read the clock chip, set the reset pin, upload configuration data from file, upload RAM data from file, gets version number,

• UC3_make_uploadfile.py: creates an .ucb file for upload. It can have multiple RAM locations and lengths.

CPLD programming

• compiling the vhdl (or verilog) code must be done on a computer with the Xilinx ISE 14.7 toolchain installed. Link: https://www.xilinx.com/support/download/index.html/content/xilinx/en/downloadNav/vivado-design-tools/archive-ise.html

• compiling itself can be done inside ISE or with the supplied makefile (look inside the bord directory in cpld firmware)

• a simple make will compile the firmware and a make prog will transfer the file to the stm32 for programming.

Used Software and OS

• Linux Mint (21.3 cinnamon) (Link: https://linuxmint.com/)
• Sublime Text 3 (Link: https://www.sublimetext.com/)
• 010 Editor (Hex Editor) (Link: https://www.sweetscape.com/010editor/)
• Chibi Studio 20 (IDE for ChibiOS) (Link: https://www.chibios.org/dokuwiki/doku.php?id=chibios:products:chibistudio:start)
• Wavedrom (2.9.1) (Link: https://wavedrom.com/)
• Pulseview (0.5.0-nightly Appimaage) (Part of sigrok) (Link: https://sigrok.org/wiki/PulseView)
• Logisim-Evolution (3.8.0) (Link: https://github.com/logisim-evolution/logisim-evolution)
• Quartus (13.0.1 Build232 Web Edition - 64 Bit) for MAX-II
• Xilinx ISE (14.7 - 64 Bit) for XC9572

Used Hardware

• Oscilloscope: Rigol DS1054Z (4 channel)
• Logic Analyzer: Hantek 4032L (32 channel)

History Lesson

The unicomp Project started a couple of years ago and is developed in my spare time. It is intended to be a module system to test out different hardware configurations or CPLD- or FPGA- extensions and to recreate old systems and test software and operating systems.

Differences Unicomp2 from Unicomp1:

• chipselect not with CPLD but with RAM on every peripheral board - more flexible,
• chipselect resolution improved to two,

Differences Unicomp3 from Unicomp2:

• chipselect RAM is on RAMROM Board (16-bit wide) - that leads to:
• simpler (and cheaper) peripheral modules,
• no linux SBC needed,
• CPLD programming from STM32 or with external programmer (JTAG Header on every CPU Module)
• 3.3V Supply on RAMROM board,
• RAM has now a backup battery (CR2032) battery,
• improved documentation.