OctobusAccp — ACCP (ND-324716 / PCB 5616) octobus controller firmware¶

The Samson ACCess Processor — the ND-5000's access processor and its octobus controller. A 68000 "baby card" with 128 KB of EPROM and 4x 8192x8 SRAM (32 KB). It supersedes ND-324702. Hardware reference: http://sintran.com/hardware/nd-5000/nd-324716.html

This folder holds the physical EPROM dump of that card's firmware — the octobus controller's operating software, previously recorded in the repo as missing (see SINTRAN\ND5000\HANDOFF-OCTOBUS-EMULATION.md line 123: "ACCP EPROM dump (68000 firmware) — would unlock full ACCP library emulation", and SINTRAN\ND5000\OCTOBUS-DEVICE-CONTROLLERS-ANALYSIS-AND-EMULATION-PLAN-2026-07-19.md section 4.3).

Layout¶

OctobusAccp/
├── README.md          ← you are here
├── eprom/             ← the raw dumps + merge/validation notes
│   ├── 51200J.bin     ← AM27C512, even bytes (D8..D15, high byte)
│   ├── 51201J.bin     ← AM27C512, odd bytes  (D0..D7, low byte)
│   ├── octo.bin       ← the two interleaved into one 128 KB 68000 image
│   └── README.md      ← interleave order, reset vectors, validation evidence
└── docs/              ← reverse-engineering writeups

The eprom/ layout follows the precedent set by the Ethernet II/III firmware at Installation\Communication\Ethernet\x\stripped\, which is the repo's other 68000-controller firmware dump.

The image¶

Property	Value
Merged image	`eprom/octo.bin`, 131,072 bytes (0x20000)
MD5	`39A21C86A74BFEDFC0B996DE7F5ADB63`
CPU	MC68000, big-endian
Ghidra language	`68000:BE:32:default`, image base `0x00000000`
Reset SSP	`0x00113FFC`
Reset PC	`0x00000BD6`
On-card SRAM	`0x00110000`–`0x00117FFF` (32 KB)

The image was validated as genuine 68000 code before use: plausible even reset vectors, a well-formed exception vector table (vectors 2..11 distinct and ascending in 0x400..0x490, vectors 12..15 sharing one handler at 0x8B8), and a cleanly disassembling entry point. See eprom/README.md for the full evidence, including why the opposite interleave order is ruled out.

Independent corroboration of the interleave: the reset code at 0x0BD6 RAM-tests 0x00110000, which is exactly the region the reset SSP 0x00113FFC points into. Two facts derived separately that agree.

Analysis¶

The reverse-engineering pass currently lives at:

E:\Dev\Ronny\NDInsight\SINTRAN\ND5000\ACCP-COMPLETE-REFERENCE.md

Its part 1 covers the identifying console strings (S A M S O N A C C E S S P R O C E S S O R, Communication ACCP-ND100 started. Version:, 6 8 0 0 0 T R A P :), the memory map, the SCN2681 DUART debug console, and the exception vector table. Parts 2-6 add the hardware address map, the console command set, the ACCP <-> ND-5000 interface seam, the CPU model class derivation, and the PIOC-OS comparison. Its companion E:\Dev\Ronny\NDInsight\SINTRAN\ND5000\ACCP-EMULATION-STATUS-AND-HANDOFF.md holds the plan, status, defects and captures. The two files absorbed twelve earlier ACCP documents on 2026-07-31.

Note on provenance: part 1 was written against the image while it still sat at C:\Temp\octo\octo.bin, so path references inside that part are stale and should point here instead. The other parts were written later and are not affected.

docs/ is reserved for further writeups so they sit next to the binary, matching the Ethernet folder's structure.

Not verified¶

The ROM base address on the real card. The vectors point at low offsets inside the image, consistent with the EPROM being mapped at 0x000000 at reset. This is an inference from the image, not confirmed against a schematic or address decoder — no ACCP schematic is present in this repo.
Whether the dumps are complete and error-free. No internal checksum or CRC word has been located, so the dumps have not been checked against any integrity value.
The firmware version. The image contains a Communication ACCP-ND100 started. Version: string but the version itself is emitted at run time; it has not been traced to a constant in the image.
What 51200J / 51201J are. These are the labels on the two physical devices. They are not ND part numbers in the usual 3xxxxx / ND-xxxxxx form and have not been matched to any ND parts list.