Wang 600 Wire ROM Readout
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Dumping, saving and assessing the microcode image
The Wire ROM from machine CC2001 was read with the custom reader using its ‘stability’ mode where each address was read 16 times and the returned data analyzed for any variations from the same address. Every address read consistently with no variations.
The complete ROM was then dumped in raw hex mode multiple times and the set of dumps passed to Doug Miller, one of a (very) few Wang microcode gurus. He was able to compare with other images in his possession and to reverse engineer the contents of the four dead addresses.
The result was a fully restored wire ROM image, known as WireROM-CC2001.
Analysis and Comparison with other ROMs
Frequency analysis on the final CC2001 image shows a pretty good utilisation of all opcodes, this is to be expected considering the cost of microcode bits.
Val AI BI ZO AOP AC BC MOP KK ST J/C JADh JADm JADl JH JL
0 1273 1255 580 1447 1241 1739 1371 899 1533 1848 804 198 172 928 945
1 21 676 59 274 807 308 72 113 26 200 1244 107 111 842 690
2 21 4 123 64 129 102 7 136 119 65 77
3 211 7 455 70 127 89 62 100 102 82 77
4 106 47 205 31 79 51 68 103 136 1 180
5 63 23 138 54 82 52 5 105 126 124 1
6 345 35 485 106 146 77 5 103 144 5 17
7 8 2 1 1 4 48 40 95 122 1 61
8 3 69 37 142 117
9 0 62 7 177 123
A 7 61 19 190 128
B 1 43 29 153 156
C 3 57 21 121 139
D 3 117 123 105 138
E 2 160 2 106 103
F 16 48 61 99 106
Test Addresses in Wire ROM
During the ROM repair process Doug Miller made a very clever observation, noticing an emerging pattern in the last four addresses even though the ROM was being improperly read and the output was plagued by noise and errors.
He hypothesised that the last four addresses were test locations:
- Address 7FC: Alternating one and zero
- Address 7FD: Alternating zero and one (ie complement of 7FD)
- Address 7FE: All ones
- Address 7FF: Mostly zeros, with the value “130” in the 3-digit JAD field
As the ROM and Reader were brought to final form, these patterns were confirmed and were very useful reassurances that the ROM was being read reliably. The complementary patterns of alternating 1s and 0s in locations 7FC and 7FD are obviously useful for bit and cross-talk tests. The all-1s address allows testing at one extreme. Address 7FF is a bit of a puzzle because it is not all zeros and the value 130 reads very consistently, it is higly likely to be a programmed value and not an error. What the 130 represents is a mystery, perhaps it is a ROM revision level, or perhaps even a serial number?
Nevertheless, it was very satisfying to see that these four locations did read as above, confirming Doug’s insight and the operation of the reader.
The WireROM-CC2001 image will be loaded into the ROM emulator and used to drive the restored machine. The Wire ROM will be left in situ for appearance but cannot be used for machine operation due to the four missing addresses
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