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MON 12B (octal) — SetCommandBuffer (SETCM)

CORRECTED 2026-07-15 (byte-verified). The worker + dispatch described below are on the DEBUNKED model and are WRONG. Byte truth from the carved L07 image: MCTAB[12B] = 005632B = SETOL=050666B in segment 003-S3CP, reached by the real dispatch MON 12B -> ENT14(072167B) -> GOTAB[12B]=MFELL(072114B) -> CALLP(032201B) -> MCTAB[12B]=SETOL. Any "GOTAB from commoncode" / "uncarved CALLPROC bridge" / "F16xx stub" / old worker name below is an artefact of the wrong table. Verified: dd if=044-S3IDPIT.bin bs=1 skip=1844 count=2 -> 51 b6. Cross-ref ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md sec 3a.

Transfers a string (up to 32 characters) into the command buffer — the buffer that holds the last command input from the terminal (you read it back by reading from logical device number 0). The parameter is fetched through the alternative page table. A common use is to erase sensitive information (e.g. password parameters) from the command buffer. This is an ND-100 monitor call.

Status: GOTAB[12B] = 000000 (byte-proven) — a fall-through: there is no direct GOTAB handler word, so the level-14 handler is reached through the resident MFELL/CALLPROC path (uncarved). There is no ND-100 code worker for this call in the carved segments: the manual short name SETCM resolves only in L07 N500-SYMBOLS (SETCM=106214B, the ND-500 companion), and the command buffer itself is the data area CBUF=170207B (L07 SYMBOL-2-LIST), which is zero-filled in this L image. So the transfer worker body cannot be read from these bytes (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User program<br/>MON 12B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[12B] = 000000<br/>(fall-through, byte-proven)"]
    C -.uncarved MFELL / CALLPROC.-> D["set-command-buffer worker<br/>(uncarved; not isolated)"]
    D --> E["CBUF command-buffer data area<br/>025-S3IRPIT :170207B (data, zero here)"]
    class A blue
    class B,C blue
    class D teal
    class E green
    classDef blue fill:#E3F2FD,stroke:#0D47A1,color:#0D47A1
    classDef teal fill:#E0F7FA,stroke:#00838F,color:#00838F
    classDef green fill:#E8F5E9,stroke:#2E7D32,color:#2E7D32

The dashed hop (C ⇢ D) is the resident MFELL/CALLPROC fall-through — it is not present in any carved segment, so it is the one link that cannot be followed statically. GOTAB[12B] is literally 000000, so there is no entry stub to disassemble; dispatch enters the resident handler. CBUF (E) is the command-buffer data destination, not the worker's code.

Code location (dispatch path)

Byte offset = (addr − loadbase) in octal words × 2 (decimal).

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[12] dispatch word commoncode.asm · .hex 071245B (1 word) 58698 GOTAB+12 = 000000 VERIFIED (fall-through)
resident MFELL/CALLPROC bridge — (uncarved) — — MFELL/CALLPROC UNVERIFIED
CBUF command-buffer data area 025-S3IRPIT.asm · .hex 170207B (1 word) 96526 CBUF DATA (zero-filled here)
SETCM (ND-500 companion) 026-S3IMPIT.asm · .hex 106214B — SETCM (N500-SYMBOLS) MISATTRIBUTED (ND-500 side, not the ND-100 body)

There is no entry-stub row: GOTAB[12] is 000000, so the level-14 handler is a resident fall-through, not a 025-S3IRPIT stub.

Verify by hand: the GOTAB word is a zero (fall-through) — grep '^71245 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex → 71245 000000 000 000 58698; confirm from the canonical bin dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=58698 count=2 2>/dev/null | od -An -tx1 → 00 00. The CBUF data word: grep '^170207 ' ../../segments-ref/025-S3IRPIT/025-S3IRPIT.hex → 170207 000000 000 000 96526; then dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=96526 count=2 2>/dev/null | od -An -tx1 → 00 00 (a stored word 000000 — the command buffer is empty/zero in this L image). prove-mon.py 12 reads the same GOTAB zero.

Instruction walkthrough

Full listing: 12B-SetCommandBuffer.ASM. There is no entry stub (fall-through dispatch) and no ND-100 worker body in the carved segments, so there is no executable walkthrough. The CBUF region is the command-buffer data area (zero here); SETCM=106214B is the ND-500 companion in 026-S3IMPIT, not the ND-100 worker.

Parameter / register contract

Manual-side names/types are from 12B_SetCommandBuffer.yaml (MAC form: LDA (CMND / MON 12, CMND, 'CLOSE-FILE 102').

Reg / field Dir Meaning Verdict
A (string addr) in address of the command string (LDA (CMND) inferred (manual)
Command in string to transfer, up to 32 characters inferred (manual)
alternative page table in the parameter is fetched through the alternative page table inferred (manual)
CBUF internal/out the command-buffer data area written to DATA (byte-located, zero here)

There is no entry stub and no carved worker, so nothing in this contract is byte-proven from executable code; every row is inferred from the manual (except that CBUF is byte-located as a data word).

Pseudo-code (for an emulator)

See 12B-SetCommandBuffer.pseudo.c — a pseudo-C model. Because the call is a fall-through and there is no carved ND-100 worker (SETCM is the ND-500 companion; CBUF is data), the model is of the documented behaviour only, NOT carved code. The fall-through MON 12 → worker bridge is modelled but not proven.

Instruction semantics follow the canonical reference: ../../instruction-semantics/ND100-INSTRUCTION-SEMANTICS.md.

Honest caveats

What is byte-proven: GOTAB[12B] = 000000 (level-14 fall-through; prove-mon.py 12 reads commoncode file byte 0xe54a = 00 00); and CBUF=170207B is a byte-located data word (000000 in this L image). That is all these carved bytes establish for this call.

What is NOT proven: anything about the transfer worker. Because GOTAB[12] is 000000, there is no stub to follow; dispatch enters the resident MFELL/CALLPROC handler in an uncarved overlay. The manual short name SETCM resolves only in N500-SYMBOLS (SETCM=106214B) — the ND-500-side companion, not the ND-100 body — so it is MISATTRIBUTED to the ND-100 call. CBUF=170207B is the command-buffer data destination (zero-filled here), not the worker's code.

This reconciles into one story: the dispatch head (GOTAB[12]=0, fall-through) is solid; the ND-100 transfer worker is not present in this carve (it is past the uncarved bridge); CBUF is the data area written to; and SETCM=106214B is the ND-500 companion. Confirming the actual worker needs a live trace (break on a real MON 12, single-step the fall-through, and record where P lands).

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md §9 · dispatch reality: ../../TASK-05-mismatches.md §G · master map: ../../MON-CALL-INDEX.md.