readme.md

ND-120/CX Microcode

The Microcode is stored in two different EPROM's each holding 8-bit of a 16 bit word

Each EPROM is 32KBytes

The PROM's 45123/45133 contains the 32 bits floating point code, the PROM's 45148/45149 contains the 48bit floating point code

AM27256_45132L = Contains the LO 8 bits (0-7) AM27256_45133L = Contains the HI 8 bits (8-15)

When creating the 64 bit microcode, you will need to read 4 addresses of 16 bits to get the

EPROM Address	Microcode bits
0	Bits 48-63
1	Bits 31-47
2	Bits 16-31
3	Bits 0-15

Microcode source code

The Source code for the microcode is available as a PDF with a total of 249 pages. Its scanned in 600 DPI and it's been OCR'ed

The ND-06.031.1 EN ND-110 and ND-120 Microprogrammer's Guide is useful for understanding the microcode.

Reading the binary microcode in C#

C# code to read the microcode into an 64bit 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)");

Schematic

Here you can se how the EPROM's was connected to the internal databuse (IDB)

EPPROM on CPU board 3202

Hex dump of Microkode

In case you just want to review the microcode as hex, here is a dump for your convinience

Hex dump