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MON 155B (octal) - GraphicFunction (GRAPH)

Executes various functions on a graphic peripheral (a NORDCOM terminal, a pen plotter, or a Tektronix display): Func 0 = PLOT, Func 1 = PLOTS (establish reference point / clear a NORDCOM screen), Func 2 = NEWP (select pen or screen). The obsolete PLOT monitor call is replaced by this. This is an ND-100 monitor call.

Status: partial. GOTAB[155B] = 122461B (byte-proven) routes to the label F1675 inside the graphic-function dispatcher cluster F1674..F1677 in overlay 025-S3IRPIT - real code. The cluster validates the Func code, then a computed jump (LDA ,B -2 / RADD SA DP) selects one of the graphic operations, each of which drives a graphic device register via IRW/IRR after a JPL-I worker call. The graphic device workers reached through the JPL-I pointer words are in the resident/runtime graphic driver, which is not in any carved segment (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User program<br/>MON 155B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[155B] = 122461B<br/>(byte-proven)"]
    C --> D["F1675 graphic dispatcher<br/>025-S3IRPIT :122461B"]
    D --> E["Code computed jump<br/>PLOT / PLOTS / NEWP + IRW/IRR"]
    E -.uncarved JPL-I pointer words.-> F["graphic device worker<br/>(resident/runtime driver)"]
    class A blue
    class B,C,D teal
    class E teal
    class F 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

GOTAB[155] enters the cluster at F1675 = 122461B. The dispatch itself (Func check, Code computed jump, IRW/IRR device-register access) is real in-cluster code. The dashed hop (E ⇢ F) is the JPL-I dispatch through the graphic worker pointer words into the graphic driver - not present in any carved segment.

Code location (dispatch path)

Every row is a real region you can open. Byte offset = (addr − loadbase) in octal words × 2 (decimal); commoncode load base is 0, 025-S3IRPIT load base is 32000B.

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[155] dispatch word commoncode.asm · .hex 071410B (1 word) 58896 GOTAB+155 = 122461B VERIFIED
graphic dispatcher (GOTAB entry) 025-S3IRPIT.asm · .hex 122461B (F1675) within 122434B-122557B 57954 F1675 (in F1674..F1677 cluster) VERIFIED (real code)
graphic worker pointer words 025-S3IRPIT.asm · .hex 122616B-122621B (data) 58140 (unnamed) real bytes = DATA
graphic device driver — (uncarved) — — graphic driver UNVERIFIED

Verify by hand (GOTAB word): grep '^71410 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex → 71410 122461 245 061 58896; then dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=58896 count=2 2>/dev/null | od -An -tx1 → a5 31 (= octal 122461, the F1675 dispatch address).

Verify by hand (F1675 entry): grep '^122461 ' ../../segments-ref/025-S3IRPIT/025-S3IRPIT.hex → byte offset 57954, value 124365; then dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=57954 count=2 2>/dev/null | od -An -tx1 → a8 f5 (= octal 124365, JMP -13, the F1675 entry word). prove-mon.py 155 reports the same GOTAB[155]=122461 -> F1675.

Instruction walkthrough

Full listing: 155B-GraphicFunction.ASM. All addresses octal; B = per-call graphic datafield (role inferred from the access pattern).

Func validation (122442-122460) — 122442 LDA ,B 4 fetches the Func code; SAT 1 / SKP IF DA UEQ ST routes Func 1 (PLOTS) through the setup worker JPL I 152 -> [122620]. The GOTAB entry F1675 = 122461 re-joins this setup path with JMP -13 -> 122446. VERIFIED (bytes).

Code computed jump (122462-122473) — 122462 LDA ,B -2 loads the Code parameter and 122463 RADD SA DP performs P = P + Code, a computed jump into the 8-entry JMP table at 122464-122473. Each entry vectors to one graphic operation arm. VERIFIED (bytes).

Graphic-register operation arms (122474-122557) — each arm calls a graphic worker (JPL I -> [122621]), stages an operand (STA ,B -7 / SHA ZIN 10), and reads or writes a graphic device register with IRW 10 D<r> (write) / IRR 10 D<r> (read, then ORA ,B -7 / IRW). The register letter cycles through A/D/L/X across the eight Code arms. The tail merges at 122557 STZ ,B -2. VERIFIED (bytes); which physical graphic register each maps to is inferred.

Worker pointer words (122616-122621) — the JPL-I targets; they disassemble as bogus instructions because they are pointer cells. Their final callees are in the uncarved graphic driver.

Parameter / register contract

Manual-side names/types are from 155B_GraphicFunction.yaml.

Reg / field Dir Meaning Verdict
Func / ,B 4 in 0=PLOT, 1=PLOTS, 2=NEWP VERIFIED fetch + Func 1 branch (122442-122446); mapping inferred (manual)
Code / ,B -2 in integer code selecting the graphic sub-operation VERIFIED computed jump (122462-122473); meaning inferred
Ycoor / Xcoor in Y/X coordinate of new line relative to reference point inferred (manual)
DeviceNo in logical device number of the graphic peripheral inferred (manual)
graphic device reg io written/read via IRW/IRR 10 D<r> per Code arm VERIFIED (122500-122556); register mapping inferred
ReturnValue out output parameter for the PLOT function (not used on ND-500) inferred (manual)

The graphic device workers reached through [122621] need live device context and are outside the carved window.

Pseudo-code (for an emulator)

See 155B-GraphicFunction.pseudo.c — a pseudo-C model for emulator authors. The Func validation, the Code computed jump, and the IRW/IRR device-register arms are byte-verified; the PLOT/PLOTS/NEWP mapping and the physical register meanings are inferred from the manual.

Every instruction in the .pseudo.c is translated against the canonical ND100-INSTRUCTION-SEMANTICS.md (RADD SA DP = P = P + A computed jump; SKP IF DA UEQ ST = if (A != T) skip; SHA ZIN 10 = logical A <<= 8; IRW 10 D<r> = reg[level 1][r] = A; IRR 10 D<r> = A = reg[level 1][r]; ORA ,B -7 = A |= mem[B-7]; bare LDA 157 = P-relative mem[P+disp], not a literal; MIN ,B -2 = increment-and-skip-on-zero).

Honest caveats

What is byte-proven: GOTAB[155B] = 122461B routes to F1675 (real code, entry word 124365 = JMP -13); the Func code fetch (LDA ,B 4) and the Func 1 (PLOTS) branch; the Code computed-jump table (LDA ,B -2 / RADD SA DP / eight JMP arms); the per-arm IRW/IRR 10 D<r> graphic-device-register access; the common tail merge at STZ ,B -2; and that 122616B..122621B are real data (pointer cells).

What is NOT proven: the PLOT/PLOTS/NEWP naming of the Func codes, the meaning of each Code sub-operation, and the graphic device workers behind the JPL-I pointer words - those live in the resident/runtime graphic driver, not present in any carved segment. The GRAPH symbol appears only in the ND-500 overlays (026-S3IMPIT/030-S3SM5), i.e. the ND-500-side graphic companion; the ND-100 handler is this F1674..F1677 cluster, attributed by the GOTAB entry + the graphic-register dispatch shape.

This reconciles into one story: the dispatch head (GOTAB[155] -> F1675) is solid; the graphic dispatcher cluster is real, fully-decoded ND-100 code that reaches graphic device registers via IRW/IRR; but its leaf workers and the exact Func/Code semantics cross the uncarved pointer/driver layer. Confirming them needs a live trace (break at 122461B on a real MON 155, single-step the RADD SA DP computed jump, and record the IRW/IRR device addresses).

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