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Wang 600 / 700 ROM Emulator

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 on UVEPROMs which 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.

The emulator has two main use cases:

Calculator Microcode Emulation

Defective microcode ROM will generally render a machine entirely dead and unresponsive. The emulator can be loaded with the appropriate original ROM image so as to replace the ROM and restore the machine.

700 Series: Changing ROM Images to Change Machine Model

The 700 series machines came in -A, -B and -C models, and two core memory sizes - 120 registers (960 steps) in 700s and 248 registers (1984 steps) in 720s. Core size is hardcoded so that 720 microcodes will run on 700 machines, but 720 microcode will fail on 700 machines due to insufficient memory. The -A and -B models differ only in microcode, while the -C models have certain hardware differences to support the -C microcode.

Changing microcode alters machine capabilities:

7x0-A 2-level subroutine stack
7x0-B 5-level subroutine stack and support for 702 plotter
7x0-C as -B, plus Block Transfer I/O devices, Binary Decisions and Learn+Run mode

600 Series: ROM options

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

Emulator Operation

The emulator must be loaded with an appropriate set of microcode EPROMs and jumpered for the host machine: Wang700, Wang600wire or Wang600mos.

The desired microcode image is selected on the emulator board and pressing PRIME on the host machine will launch that image. There are no other controls and the emulator can be installed inside the chassis and left alone unless a different microcode image is wanted.