Wang 600-14TP #CC7681

This 600-14TP #CC7681 represents the final iteration of the original Wang 700 logic engine, physical design and form-factor. Wang had moved to larger-scale integration and smaller form factor with the 400 series, although too little and too late to remain competitive with HP, TI and many others. Wang was moving on from the calculator business in the 1970s but demand for the 600 series must have persisted, this 600-14TP #CC7681 has date codes from late in 1977 and most likely represents one of the last 600 machines, with some final updates and improvements.

For a more detailed discussion of the technical design and construction of the Wang 600, see the entry for the Wang 600-6TP.

Hardware and Power

Wang 600 General Construction (opens in new tab)

The chassis, construction methods and layout remain the same as the early 600 machines, in turn as inherited from the 700 series. There is still have an uncomfortable mixing of mains and low voltages on the motherboard PCB. The power supplies are simple with a multi-tap transformer feeding linear regulators. Pass-transistor failure is unmitigated and continues to threaten hundreds of ICs.
During restoration, the mains wiring has been revised to separate it from low-voltage, and volt clamps added to vulnerable circuits as noted below.

Keyboard

It is surprising to note the absence of Wang’s signature short-travel ‘clicky’ keyboard built with generic industrial microswitches, used unchanged in the initial LOCI machines of the early 1960s, all of the 300 series, all of the 700 series, and carried into the first 600 machines, a seen in DoPECC’s 600-6TP machine.

The new keyboard has long-travel keys with more conventional ‘keyboard feel’ and nice rounded ‘keyboard-style’ keytops. The keys are still labelled with cutout paper labels, maintaining at least one link right back to the LOCIs.

The new keyboard has a nicer ‘feel’ but represents a significant investment in engineering and metalwork for a machine that Wang must have been known to be on its last legs.

Electronics

The electronics package remained essentially the same for all 600 series - approximately 250 SSI ICs, mostly from the 74xx TTL family with a few 99xx DTuL packages. These implement a bit-serial processor with 1-bit wide ALU, driven by a 4Mhz clock to process 400,000 microinstructions/second. There is little or no helper hardware: display refresh, print hammer timing, tape data recording and data extraction are performed entirely by microcode.

The ALU has been modified from the early 600 machines, the 5964 board has become 6192, which is not found in any documentation. Reverse engineering shows extra microcode decoding to generate a digital signal for the formerly unassiged Z-bus address of 7. This new signal is exposed on the 6192 edge connector, but is not routed on the motherboard and therefore cannot be used, even by custom microcode. Further investigation reveals that the 6192 ALU was used in the Wang 1200 word processor and it’s likely that the Z=7 signal was used in the 1200. Since the 1200 was in active production in the late 1970s when the 600 was being retired, perhaps the final 600s were given 6192 ALUs, allowing production of the older ALUs to end

A volt clamp has been added to the main +5 rail to protect the hundreds of ICs that would be at risk from a pass-transistor short.

Microcode

This machine has MOS ROM for microcode, rather than the delicate and expensive wire-braid ROM used in 700 and early 600 series machines. Microcode size remains 2k x 42-bit words and eleven Signetics 2580 PMOS 2k x 4 mask-programmable ROMs are used. The resulting ROM board is one-third the size of the wire-braid version and very much more robust.

A DoPECC ROM Emulator is mounted into some of the space available in the original ROM chassis. The original ROM can still be used, or the chassis can be rotated to allow the emulator to be plugged in if diagnostic routines are required.

The Signetics ROMs require a -13v supply that is generated on the MOS ROM PCB by a series-pass regulator. The ROMs are precious and a voltage clamp has been added to the ROM board to protect the ROM chips from -13v regulator failure. The +5 supply to these chips is protected by a volt clamp on the main machine +5 supply.

RAM

This late-production machine has a revised RAM board that uses Intel 2012 1k x 1 ICs in place of the Mostek Mk4008s used in early machines. The 2102 is a static RAM and requires only +5v. This allows a considerable simplification of the RAM board by eliminating the the refresh counter with its associated gating, and the transistor switches used to reduce RAM power dissipation. The main use for the well-regulated -13v supply is also lost but the supply is retained for the ROM expansion socket, where MOS ROMs requiring -13v may be attached.