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Wang Calculator ROM Reader

The Wang Wire Braid ROMs are now fifty or more years old. They were fragile when first made and operated near to their technical limits, requiring individual adjustment for optimal performance. It’s quite reasonable to be apprehensive about the operating state of any such ROM today. Furthermore, since all functions of the Wang 600 and 700 machines are generated by microcode, a single bad bit in a critical area can bring down the entire machine and render it dead and unresponsive.

With these considerations in mind, it was easy to seen the need for a stand-alone ROM reader that could

  • dump the contents of a ROM and
  • exercise the ROM to test if it was reading consistently.

DoPECC is keen to build a library of Wang Calculator Microcodes. When used with the DoPECC ROM Emulator these codes allow matching machines with defective ROM to be restored. If you have ROMs that you are interested to read, see below for details of how to obtain and use the ROM Reader

ROM Reader Design

Wang ROM Reader
Wang ROM Reader
The ROM Reader is based on a PIC microcontroller which emulates the ROM drive signals from the 700 and 600 calculators. These have different ROMs with different electrical interfaces and different drive requirements.

Other than the Reader, users must have:

  • a computer with serial port and terminal software, eg a common USB-serial dongle and PuTTY
  • two clean, well-regulated power supplies:
    • +5v @ 700mA
    • +16v (for 600) or +12v (for 700) @ 100mA

The 600 series ROM is simpler to read because it has on-board latches which capture and hold the ROM outputs between ROM drive cycles. After setting up an address and applying the drive signals in correct sequence, the microcontroller can scan the 42 output bits in groups of 8 to acquire a complete microcode word.

Wang ROM Latches
Wang ROM Latches
The 700 series ROMs require an additional latch board between the ROM and the Reader because the 700 ROM has a pulsed output, only emitting data for the duration of the ROM drive cycle. The latches are necessary to capture and store the pulses until the microcontroller can read the complete microcode word.

ROM Reader Jumpers

Prior to applying power, set the jumpers to the type of ROM to be read:

  • JP3: Wang 700 1-2, Wang 600 2-3
  • JP4: Wang 700 1-2, Wang 600 2-3
  • JP5: Always 2-3

ROM Reader Setup

The Reader interfaces to a host PC by TTL-level serial interface at 96008N1. To interface via USB, use any common USB-serial dongle. No host software is required other than a terminal emulator such as PuTTY.

Two power supplies are required:

  • 5v for Reader logic and ROM logic. This can be applied continually.
  • Memory Drive +16v for 600 series and +12v for 700 series. This must be applied if the ROM is to be read but can be removed for other tests.

Removing the Memory Drive supply protects the ROM wires from damage if there is a fault that may cause the ROM drive to be stuck ‘on’, potentially overloading the address wire(s).

Note that the ROM is vulnerable to noise, quiet power supplies should be used (beware poor quality switching supplies). Separate digital and memory sense grounds are provided and these should be routed separately to the power supply.

Apply +5v and verify that a sign-on message appears. Check that the first character of the prompt is a ‘6’ or a ‘7’ according to the jumper settings selected above. Enter ‘?’ and verify that the input is seen and the help text appears.

ROM Reader Operation

Reading Wang 600 ROM
Reading Wang 600 ROM
The reader can operate in two modes:

  • H = Hex dump mode. Microcode is read and dumped to secreen, one address per line
  • S = Stability mode. Each address is read 16 times and the results of a consistency analysis are shown

The mode is shown in the second character of the prompt. Enter H or S to change the mode.

Reading occurs from the address displayed in the prompt. To change address:

  • enter up to three hex digits and CR
  • enter ‘<,’ to decrement, ‘>.’ to increment
  • enter CR on a blank line for address zero

Reading Wang 600 ROM
Reading Wang 600 ROM
To read the ROM according to mode H or S as above, select a single or repeated read command:

  • R = single read. Repeated presses will re-read same address
  • Z = read, increment and repeat until end of ROM (address 7FF)

ROM Reader Available For Use

The ROM Reader hardware is available for anyone who wants to test or dump their ROMs.

Blank PCBs are available for anyone who wants to build their own, or a functional reader is available for loan, for the cost of postage.

Please contact via About&Contact for further information