85605-A-2 Sheet 2/8 — I/O PORT

manual p24 · 11 ICs · 11 verified ✓ · layout mirrors the original drawing
Click a net label to trace it — endpoints colour-coded input · output · in/out — click an IC box (either panel) to select it in both, click again to deselect (multi-select OK), Esc clears all. Use the IC rail on the far left to jump straight to a chip. A net name shown muted like this and prefixed $ is ours - a node the 1985 drawing leaves unlabelled; every other name was read off the drawing. Hover a pin for its net's story.
Interboard connectors (the band cables between the boards) — circled letter+number labels on the drawing are connector row + pin
3B — 74LS139: C000-DFFF splitter (2kB blocks on AB11/AB12, gated by /CSCD from 1/8). Y1 = the shared C800 select: to 7B locally AND out as /C8CS (B13) for the C board scroll registers. Only the first decoder half is used; the second half (pins 9-15) is drawn nowhere and has no tracks on the board. — verified 2026-07-25 3B ✓ 74LS139 /CSCD · <- sheet 1/8: C000-DFFF select ~G1 1 /CSCD AB11 A1 2 AB11 AB12 B1 3 AB12 /$C0XX · C000-C7FF -> read decoder 3A Y0 4 /$C0XX /C8CS · C800-CFFF -> CN-1 B13 (also C board) Y1 5 /C8CS /D0CS · D000-D7FF Y2 6 /D0CS /D8CS · D800-DFFF -> CN-1 B14 (scroll VRAM, verified from C side) Y3 7 /D8CS GND:8=GND VCC:16=+5V 3A — 74LS138: Read strobes IN0-/IN5 = C000-C005 reads (qualified by /RDB) — verified 2026-07-25 3A ✓ 74LS138 AB0 A 1 AB0 AB1 B 2 AB1 AB2 C 3 AB2 /$C0XX · <- 3B pin 4 (C000-C7FF) ~G2A 4 /$C0XX /RDB · read strobe - ports answer only on reads ~G2B 5 /RDB +5V G1 6 +5V /IN5 · C005 read -> a2-custom 6N pin 9 (resets the 10M decryptor) Y5 10 /IN5 IN4 · -> 2B pin 19 (DSW2 ~OE) | drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so Y4 11 IN4 IN3 · -> 2A pin 19 (DSW1 ~OE) | drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so Y3 12 IN3 IN2 · -> 5B pins 1+15 | drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so Y2 13 IN2 IN1 · -> 4B pins 1+15 | drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so Y1 14 IN1 IN0 · -> 6B pins 1+15 | drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so Y0 15 IN0 GND:8=GND VCC:16=+5V 7B — 74LS138: Write strobes C800-C807 (138). G2A = AB3 so C808+ is left to the C-board scroll registers. Only three outputs are used: Y0 = OUT0 (C800, sound-command latch -> 3/8 8J pin 11), Y4 = OUT4 (C804, control register -> 7A pin 9), Y6 = /OKOUT (C806, sprite DMA -> CN-1 B20). The other five are decoded but go nowhere - confirmed on the board for pins 7 and 10. Not /WRB-qualified by design. — verified 2026-07-25 7B ✓ 74LS138 AB0 A 1 AB0 AB1 B 2 AB1 AB2 C 3 AB2 AB3 · the split: only C800-C807 stay on A, C808+ -> C board ~G2A 4 AB3 /C8CS · <- 3B pin 5 ~G2B 5 /C8CS +5V · write NOT gated here by design G1 6 +5V $OUT7 · unused - no pad connection on the board (checked 2026-07-27); agrees with MAME, which writes only C800/C804/C806 in this range Y7 7 $OUT7 /OKOUT · C806 sprite-DMA trigger -> CN-1 B20 (to B board) Y6 9 /OKOUT $OUT5 · unused - no pad connection on the board (checked 2026-07-27); agrees with MAME, which writes only C800/C804/C806 in this range Y5 10 $OUT5 OUT4 · C804 control-register write -> 7A pin 9 (CLK). Name joined 2026-07-27 (138 outputs are active low) | drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so Y4 11 OUT4 $OUT3 · unused - MAME writes only C800/C804/C806 in this range; pins 7 and 10 of the same decoder were physically confirmed unconnected Y3 12 $OUT3 $OUT2 · unused - MAME writes only C800/C804/C806 in this range; pins 7 and 10 of the same decoder were physically confirmed unconnected Y2 13 $OUT2 $OUT1 · unused - MAME writes only C800/C804/C806 in this range; pins 7 and 10 of the same decoder were physically confirmed unconnected Y1 14 $OUT1 OUT0 · C800 sound-command write -> 3/8 sound latch 8J pin 11 (CLK). Joined 2026-07-27; was mis-named /C800 here while the sound sheet called it /OUT0 | no overbar on the sheet (Robert, 2026-07-27) Y0 15 OUT0 GND:8=GND VCC:16=+5V 7A — 74LS174: Control register C804 (MAME c804_w): DB0/DB1 -> coin counters (TR2/TR3 C2120 drivers), DB4 -> sound CPU reset (TR1 C945 -> /CPUBRES to 3/8), DB7 -> FLIP (6/8, 7/8 + CN-2 D2). Cleared by /ACL1 — verified 2026-07-25 7A ✓ 74LS174 /ACL1 · ~CL <- 11J pin 4 via CN-1 B19. Continuity to 11J.4 confirmed 2026-07-25 ~CL 1 /ACL1 DB1 D2 4 DB1 DB0 D3 6 DB0 OUT4 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so CLK 9 OUT4 DB4 D4 11 DB4 DB7 D5 13 DB7 $CNTR2 · -> R19 470R (+R22 470R to GND) -> TR3 -> 4/8 + edge a COUNTER2 Q2 5 $CNTR2 $CNTR1 · -> R20 470R -> TR2 -> edge 23 COUNTER1 Q3 7 $CNTR1 $SRESDRV · -> R21 1K -> TR1 (C945) -> /CPUBRES to sound 3/8; other leg GND Q4 10 $SRESDRV FLIP · screen flip -> 6/8, 7/8 + CN-2 D2 (C-side verified) Q5 12 FLIP GND:8=GND VCC:16=+5V 6B — 74LS367: SYSTEM port, read at C000 (IN0): selects, coins, two spare bits. RA4 1Kx8 pullups + RC filtering on every input — verified 2026-07-25 6B ✓ 74LS367 IN0 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~EN1 1 IN0 COIN2 · edge V via R15 A1 2 COIN2 $SWU · $SWU spare <- R13 -> edge U (D5) A2 4 $SWU $SEL2P · edge T via R17 A3 6 $SEL2P COIN1 · edge 18 via R14 A4 10 COIN1 $SEL1P · edge 16 via R18 A5 12 $SEL1P $SW17 · $SW17 spare <- R16 -> edge 17 (D4) A6 14 $SW17 IN0 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~EN2 15 IN0 DB7 Y1 3 DB7 DB5 Y2 5 DB5 DB1 Y3 7 DB1 DB6 Y4 9 DB6 DB0 Y5 11 DB0 DB4 Y6 13 DB4 GND:8=GND VCC:16=+5V 4B — 74LS367: P1 controls read at C001 (IN1): RIGHT1->DB0, LEFT1->DB1, SHOT1->DB4, SHOT2->DB5, DOWN1->DB6, UP1->DB7 (DB2/DB3 unused). 220R series + 1Kx8 pullups — verified 2026-07-25 4B ✓ 74LS367 IN1 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~EN1 1 IN1 UP1 · edge 11 A1 2 UP1 SHOT2 · edge 9 A2 4 SHOT2 LEFT1 · edge 13 A3 6 LEFT1 DOWN1 · edge 12 A4 10 DOWN1 RIGHT1 · edge 14 A5 12 RIGHT1 SHOT1 · edge 10 A6 14 SHOT1 IN1 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~EN2 15 IN1 DB7 Y1 3 DB7 DB5 Y2 5 DB5 DB1 Y3 7 DB1 DB6 Y4 9 DB6 DB0 Y5 11 DB0 DB4 Y6 13 DB4 GND:8=GND VCC:16=+5V 5B — 74LS367: P2 controls read at C002 (IN2), mirrors 4B: $RIGHT2->DB0, $LEFT2->DB1, $SHOT1B->DB4, $SHOT2B->DB5, $DOWN2->DB6, $UP2->DB7. Edge pins K-R (solder side) — verified 2026-07-25 5B ✓ 74LS367 IN2 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~EN1 1 IN2 $UP2 · edge M (JAMMA solder side, P2) A1 2 $UP2 $SHOT2B · edge K (JAMMA solder side, P2) A2 4 $SHOT2B $LEFT2 · edge P (JAMMA solder side, P2) A3 6 $LEFT2 $DOWN2 · edge N (JAMMA solder side, P2) A4 10 $DOWN2 $RIGHT2 · edge R (JAMMA solder side, P2) A5 12 $RIGHT2 $SHOT1B · edge L (JAMMA solder side, P2) A6 14 $SHOT1B IN2 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~EN2 15 IN2 DB7 Y1 3 DB7 DB5 Y2 5 DB5 DB1 Y3 7 DB1 DB6 Y4 9 DB6 DB0 Y5 11 DB0 DB4 Y6 13 DB4 GND:8=GND VCC:16=+5V 2A — 74LS245: DSW1 reader (C003, IN3): DIP SW (A) contacts onto the DB bus. DIR grounded = B->A only — verified 2026-07-25 2A ✓ 74LS245 GND DIR 1 GND $SWA8 B8 11 $SWA8 $SWA7 B7 12 $SWA7 $SWA6 B6 13 $SWA6 $SWA5 B5 14 $SWA5 $SWA4 B4 15 $SWA4 $SWA3 B3 16 $SWA3 $SWA2 B2 17 $SWA2 $SWA1 B1 18 $SWA1 IN3 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~G 19 IN3 DB0 A1 2 DB0 DB1 A2 3 DB1 DB2 A3 4 DB2 DB3 A4 5 DB3 DB4 A5 6 DB4 DB5 A6 7 DB5 DB6 A7 8 DB6 DB7 A8 9 DB7 GND:10=GND VCC:20=+5V 1A — DIP-SW8: DIP SW (A) = DSW1 (coinage/lives per MAME). Contacts 1-8 with RA1 2.2Kx8 pullups; commons 9-16 grounded. Board position vs 1B provisional — verified 2026-07-25 1A ✓ DIP-SW8 $SWA1 S1 1 $SWA1 $SWA2 S2 2 $SWA2 $SWA3 S3 3 $SWA3 $SWA4 S4 4 $SWA4 $SWA5 S5 5 $SWA5 $SWA6 S6 6 $SWA6 $SWA7 S7 7 $SWA7 $SWA8 S8 8 $SWA8 C8:9=GND C7:10=GND C6:11=GND C5:12=GND C4:13=GND C3:14=GND C2:15=GND C1:16=GND 2B — 74LS245: DSW2 reader (C004, IN4): DIP SW (B) onto the DB bus. RA10 2.2Kx8 sits on the DB bus itself — verified 2026-07-25 2B ✓ 74LS245 GND DIR 1 GND $SWB8 B8 11 $SWB8 $SWB7 B7 12 $SWB7 $SWB6 B6 13 $SWB6 $SWB5 B5 14 $SWB5 $SWB4 B4 15 $SWB4 $SWB3 B3 16 $SWB3 $SWB2 B2 17 $SWB2 $SWB1 B1 18 $SWB1 IN4 · drawn WITHOUT an overbar on the sheet (Robert, 2026-07-27); the strobe is still active-low by construction, the name just does not say so ~G 19 IN4 DB0 A1 2 DB0 DB1 A2 3 DB1 DB2 A3 4 DB2 DB3 A4 5 DB3 DB4 A5 6 DB4 DB5 A6 7 DB5 DB6 A7 8 DB6 DB7 A8 9 DB7 GND:10=GND VCC:20=+5V 1B — DIP-SW8: DIP SW (B) = DSW2 (difficulty etc. per MAME). RA5 2.2Kx8 pullups; commons grounded. Board position vs 1A provisional — verified 2026-07-25 1B ✓ DIP-SW8 $SWB1 S1 1 $SWB1 $SWB2 S2 2 $SWB2 $SWB3 S3 3 $SWB3 $SWB4 S4 4 $SWB4 $SWB5 S5 5 $SWB5 $SWB6 S6 6 $SWB6 $SWB7 S7 7 $SWB7 $SWB8 S8 8 $SWB8 C8:9=GND C7:10=GND C6:11=GND C5:12=GND C4:13=GND C3:14=GND C2:15=GND C1:16=GND
· Original scan — manual p24 · zoom
original schematic scan
3B
3A
7B
7A
6B
4B
5B
2A
1A
2B
1B