MON 174B (octal) — UserDef4 (US4)

An installation/user-definable monitor call. SINTRAN III reserves eight slots (170B–177B, names UserDef0–UserDef7, short US0–US7) that a site may implement itself. No handler for MON 174B is installed in this SINTRAN L image, so there is no code body to disassemble — this document records that proven absence and how a site would install one.

Status: dispatch-table structure byte-proven — the level-14 MGOTA table ends at MON 161B, so MON 174B has no dispatch-table entry at all (it is past the table's end). No worker is carved or fabricated. All addresses/values are octal.

• No per-call disassembly: MON 174B is a user-definable slot with no installed handler in this image; there is nothing to disassemble, so no 174B-UserDef4.ASM/.pseudo.c is fabricated.
• Bytes live once in the canonical segment layer: ../../segments-ref/.

---

Dispatch path

flowchart LR
    A["User program<br/>MON 174B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["MGOTA table ends at MON 161B<br/>MON 174B has NO table entry"]
    C -.site must install.-> D["DEFINE-USER-MONITOR-CALL<br/>+ MAC code after 7ENDC"]
    D -.none installed in this L image.-> E["undefined in this image<br/>(UNVERIFIED runtime)"]
    class A blue
    class B,C teal
    class D,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 MGOTA MON-dispatch table (base 071233B, one word per MON number) runs cleanly from MON 0B to MON 161B — odd MON numbers carry an F16xx level-14 entry stub, even MON numbers carry 000000 (fall-through). The last real entry is MON 161B at 071414B (F1677). The word at 071233B + 174B = 71427B lies past the end of the dispatch table, inside the adjacent D1700/E1600 device- and interrupt-ident data block that begins at 071416B. So MON 174B has no level-14 handler address here; a site installs one with DEFINE-USER-MONITOR-CALL.

---

Code location (dispatch path)

Byte offset = (addr − loadbase) octal words × 2; MGOTA base = 071233B in commoncode (load 0).

Role	Segment (full disasm)	Addr (octal)	Byte offset	Reads	Verdict
word at 071233B+174B	commoncode.asm · .hex	71427B (1 word)	58926	000000 (device/ident-table zero fill)	documented-absent (zero)
installed handler (site)	— (not in this image)	—	—	after 7ENDC, via DEFINE-USER-MONITOR-CALL	UNVERIFIED (none installed)

Verify by hand: grep '^71427 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex → byte offset 58926; then dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=58926 count=2 2>/dev/null | od -An -tx1 → 00 00 (= octal 000000). Compare the last real table entry: grep '^71414 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex → F1677 = MON 161B, the final MON-dispatch slot; everything at 071415B+ is device/ident data, not the MON table.

---

Instruction walkthrough

There is no instruction body to walk — that is the point of this entry. MON 174B is one of the eight user-definable slots and no handler is installed in this SINTRAN L image. The word the naive 071233B + 174B index lands on (000000) belongs to the neighbouring device/ident data, not to a MON handler, so it is not disassembled as code.

---

Parameter / register contract

Per the manual (Developer/MON/calls/174B_UserDef4.yaml): both input and output parameters are user-defined — a site transfers them the same way as SuspendProgram / InString / WriteToFile. Nothing is byte-proven here because no handler exists in this image.

Reg / field	Dir	Meaning	Verdict
T	in	MON number (174B) used to index the level-14 table	VERIFIED (dispatch mechanism)
args	in/out	entirely user-defined (site convention)	UNKNOWN — no installed handler
skip / status	out	user-defined by the site handler	UNKNOWN — no installed handler

Installation notes (from the manual): patch the handler's MAC instructions into physical memory after the SINTRAN symbol 7ENDC (best from a mode file — the call is lost on a warm start), then register its entry with the SINTRAN-SERVICE-PROGRAM command DEFINE-USER-MONITOR-CALL. If the TPS subsystem is installed, user calls 170B–175B may not be available.

---

Honest caveats

What is byte-proven: the shape of the level-14 MGOTA dispatch table. It holds one word per MON number from 071233B and its last real entry is MON 161B (071414B = F1677); MON 162B onward is the adjacent D1700/E1600 device/interrupt-ident data block (starts 071416B). MON 174B therefore has no dispatch-table entry. The word at 71427B reads 000000 — a zero fill that is coincidental table data, not a MON 174B handler.

What is NOT proven / not present: any handler body for MON 174B. These are user-definable slots; none is installed in this L image (the SINTRAN symbol 7ENDC, after which a site would place its code, bounds the resident image — the user area beyond it is empty here). No .ASM/.pseudo.c is fabricated. Recovering a real body would require an image where a site had actually installed the call. There is no contradiction to reconcile: the eight 170B–177B slots are all in the same state — defined by the architecture, unimplemented in this image.

---

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