The complete microcode of the Norsk Data ND-120 "DELILAH" CPU — as EPROM dumps, as a 600 DPI scan of the original 1987 printed listing, and (the crown jewel) as fully reconstructed, compilable assembly source recovered from that scan and proven bit-for-bit against the silicon.
| File | Version | What it is |
|---|---|---|
| ND-120-DELILAH-K.LISTING.txt | K (oct 13) | The printed listing, re-typed from the scans — every line number, label, comment and instruction |
| nd-120-delilah-K.uc | K | The same source, compilable with the ND110Compile assembler |
| ND-120-DELILAH-L.LISTING.txt | L (oct 14) | Version L, derived from K by applying ND's own changes |
| nd-120-delilah-L-from-K.uc | L | Compiles bit-exact against the EPROM dump — all 4886 words |
The printed listing is version K; the EPROMs in the machines are version
L. It took a long OCR-correction campaign (every suspect line verified
against the page scans) to get here, and the payoff is the full K→L diff:
Norsk Data bumped the version word, inserted one COMM,SLOW word in the
CPU-init sequence, removed the P/B/X register-read delay (an assembler
token-table change — no source lines touched), adjusted six condition-false
sequencing specs, and made four small operand fixes. 13 changed source lines
in total, and every jump label identical — that is the entire difference
between the two ROMs.
The reconstruction pipeline, gates and the full change-log live in the
ND120UC repo (external repository, not in this tree) (docs/K-to-L-source-changes.md).
The microcode is stored in two 32 KByte EPROMs, each holding 8 bits of a 16-bit word:
- AM27256_45132L — LO 8 bits (0–7)
- AM27256_45133L — HI 8 bits (8–15)
The 45132/45133 pair contains the 32-bit floating point code; the 45148/45149 pair contains the 48-bit floating point code.
Each 64-bit microcode word is built from 4 consecutive 16-bit reads:
| EPROM Address | Microcode bits |
|---|---|
| 0 | Bits 48–63 |
| 1 | Bits 32–47 |
| 2 | Bits 16–31 |
| 3 | Bits 0–15 |
The low byte of the word at octal address 020 is the microcode version: oct 13 = K, oct 14 = L.
C# code to read the microcode into a 64-bit wide array named chip_microcode:
byte[] LOBits = File.ReadAllBytes("AM27256_45132L.bin");
byte[] HiBits = File.ReadAllBytes("AM27256_45133L.bin");
ulong[] chip_microcode = new ulong[1024 * 64];
int cnt = 0;
for (int i = 0; i < HiBits.Length; i += 4)
{
ulong uc = 0;
for (int b = 3; b >= 0; b--)
{
ushort w = (ushort)(HiBits[b + i] << 8 | LOBits[b + i]);
uc = uc << 16;
uc |= (ushort)w;
}
string ucHex = $"{uc:X16}".PadLeft(16, '0');
string addr = Convert.ToString(cnt, 8).PadLeft(6, '0');
Console.WriteLine($"i={i}, uC[{addr}]: {ucHex}");
chip_microcode[cnt++] = uc;
}
ushort version = (ushort)(chip_microcode[0x10] & 0xFF);
Console.WriteLine($"Version is {Convert.ToString(version,8)} (octal)");- ND-120 Mikroprogramlisting-L-ocr.pdf — the original printed listing (version K), 249 pages, scanned at 600 DPI. The source of truth the reconstruction was verified against.
- ND-06.031.1 EN ND-110 and ND-120 Microprogrammer's Guide — the reference for understanding the microcode word format and tokens.
Here you can see how the EPROMs were connected to the internal data bus (IDB):
In case you just want to review the microcode as hex, here is a dump for your convenience: Hex dump