Wang 600 / 700 ROM Emulator

ROM emulator for Wang 600, Wang 700 calculators (opens in new tab)

The ROM Emulator has been developed to solve the problem of Wang 700 and 600 machines that are dead due to defective microcode ROM. The Emulator is directly plug-compatible with all models of 700 and 600 machines, is powered by the existing wiring and can be fitted into the chassis of all machines without modifications.

The Emulator is based EPROMs, UV erasable 27256 or electrically erasable 28256 types. These can hold up to 16 2k word ROM images, any one of which is selected by a rotary switch. It is simple to mount this switch so that images can be changed on the fly.

ROM Emulator Schematic (opens in new tab) can be viewed at this link.

The emulator has two main use cases:

Calculator Microcode Emulation

Defective microcode ROM will generally render a machine entirely dead and unresponsive. Replacing the ROM with the plug-compatible emulator can restore the machine but it’s important to select a compatible ROM image.

700 Series

Wang 700 with ROM Emulator (opens in new tab)

The 700 series machines came in two memory sizes and three microcode variants. Memory size relates to model number:

700 has 120 registers/960 steps
720 has 248 registers/1984 steps

Microcode variants are:

-A 2-level subroutine stack
-B 5-level subroutine stack and support for 702 plotter
-C as -B, plus Block Transfer I/O devices, Binary Decisions and Learn+Run mode

The -A and -B models have identical hardware while -C models have modifications to three logic boards and the backplane wiring.

Smaller memory ROMs will run on larger memory machines but not vice versa. -A and -B microcode is interchangable but -C microcode requires -C hardware.

600 Series

ROM Emulator Installation (opens in new tab)

Memory size is hardcoded in the 600 series with specific ROMs for 1K, 2K and 4K machines. Smaller ROMs will run on larger machines, but not vice versa.

The only ROMs known are for machines with printers, it’s likely that non-printer machines would have had specific ROM. Otherwise, no other functional variations are known.

DoPECC is keen to obtain ROM Images from other machines, see the ROM Reader page for further details.

Diagnostic Microcode for Troubleshooting

The calculator microcode is complex and generates all machine behaviors including display refresh. Microcode errors and machine hardware faults all tend to have the same symptom of ‘dead machine’ with no further useful symptoms available to assist with diagnosis.

The emulator allows a series of diagnostic microcodes to be loaded and run. These test well-defined parts of the machine hardware in a manner that is easy to test and verify, allowing the hardware to be systematically exercised and verified. Fault finding is much faster and easier as a result.

Diagnostic routines include:

Single Instruction Loop - tests basic timing and data bus function
Memory Address Loop - tests memory addressing
Display - tests display, memory read and ALU branching
Conditionals - tests ALU conditional branches
Memory Test - tests read/write from all memory locations
Keyboard - tests keypresses and switches, shows codes on display

See the Repair Tools section for each machine family for machine-specific diagnostic microcode information

Emulators in Use

Wang 700A

As can be seen in the picture, the emulator fits behind the PCB stack, the ROM connector wiring can be routed through existing chassis slots and the ROM image selector is accessible through the fan opening. This is quite a nice arrangement.

Wang 600

It is not possible to mount the emulator on top of the chassis (like the 700 above) without substantial metalwork to make a passage for the ROM cables. The next-best option seems to be as shown, placing longer bolts in existing mounting holes and mounting the emulator as shown. The image selector is mounted off-board using new holes drilled in the rear flange bracket.

Obtaining an Emulator

DoPECC is keen to keep Wang 600 and 700 machines alive.

Emulators are available as bare PCBs or fully built-up with EPROM sets as needed, cost is simply that of parts and shipping.

Please use the About&Contact link for further details.