First Power with ROM Emulator
The logic boards were examined as they were loaded back into the chassis. All were in good condition with no corrosion or other damage. Particular observations were:
- The 6182 ROM address board had replacements for two ICs:
- L7 8266B 4-bit multiplexer, an unusual type
- L29 7474 dual flipflop
- the 5965 timing and tape board had one replacement IC:
- L17, 7404 hex inverter
With no obvious defects found, the boards were loaded into the chassis ready for first attempt at power-up
Microcode ROM Emulator
ROM Emulator installed
DoPECC has yet to find an original Wang wire braid microcode ROM that is fully functional and can support calculator operation. While only a handful of bits may be defective in any ROM the density of the microinstructions and the density of the microcode coding needed to pack the calculator’s functionality into 2k or fewer words means that the loss of even a few bits is fatal to calculator operation.
Therefore, a DoPECC ROM emulator has been fitted into the narrow space between motherboard and wire ROM. The ROM wiring harness is easy to connect and the wire ROM can be left in original position. The emulator can hold up to 16 ROM images, allowing 1,2, and 4K microcode to be run, and a variety of custom diagnostic microcodes.
First Run - signs of life only
Selecting a Wang 600 microcode image we find:
- PRIME after short delay the LHS + sign lights
- SET PC Prog Error lights and LHS + sign lights
- VERIFY Prog Error lights, short delay, then LHS + sign lights
- RECORD Tape relay activates, LHS + lights brightly, then LHS DP lights, then relay deactivates and LHS + sign becomes dimmer
These results are useful, they show that some sequences of microinstructions are executing, suggesting that that clocks and some logic engine functions are at least somewhat working. To gain further information it’s useful to try some of the diagnostic microcodes that are available in the ROM emulator.
Diagnostic Microcode
These diagnostics (among others) are built into the ROM emulator, so it’s easy to begin diagnosis when full calculator microcode fails.
BASEdisp
This is a fairly simple code that increments the three 4-bit memory address registers and uses these counters to:
- address 16 sequential locations of RAM and
- loop for a period on each address The loop-on-same-address causes the display to unblank, so successful execution of this simple code will light the display with whatever random data is present in the RAM.
This test failed - no display
BASEv1
This is the simplest microcode test - a single microinstruction that increments the V register and loops to itself, causing an endless 4-bit count. The test must be monitored with an oscilloscope or similar.
This test passes
BASEvut
This is a more complex code that uses the three memory address registers U, V, T as a 12-bit counter with carry-out from each register generating the increment of the next register. Again, the result must be observed with an oscilloscope or logic analyzer.
This test fails: counts occur in T and V but U is always zero
The results above suggest that the V register may be faulty.
The best way to investigate such a fault is with the DoPECC 2-word ROM. This device allows specific microinstructions to be set up and then altered so as to test specific circuit pathways.