Commodore Plus/4 & C16 (TED Series) Hub
Commodore 264-family workbench reference — 7501/8501 CPU & 7360/8360 TED thermal protection, C16 9 V centre-negative & Plus/4 square DIN PSU alerts, C16 64K RAM upgrade, and Mini-DIN joystick/tape pinouts.
MOS 7501/8501 CPU & 7360/8360 TED Thermal Failure + Joystick ESD Red Alert!
The Commodore 16, C116, and Plus/4 rely on two custom HMOS integrated circuits that have the highest thermal and ESD failure rate of any 8-bit Commodore chips: the 40-pin MOS 7501 / 8501 CPU and the 48-pin MOS 7360 / 8360 TED (Text Editing Device). Because the TED chip combines the video controller, 121-colour generator, DRAM refresh multiplexer, dual timers, sound generator, AND keyboard/joystick latch onto a single die running up to 1.77 MHz — and because Commodore wired the 8-pin Mini-DIN Joystick ports directly to the TED chip's data bus pins with zero buffer ICs or clamping diodes — running a C16/Plus/4 without heatsinks or hot-plugging a joystick will destroy the TED or CPU in seconds!
1 Mandatory Heatsink & RF Cage Fix
- Ditch the Spring-Tab Tin Shield Lid (or Add Copper Heatsinks): From the factory, Commodore pressed two stamped tin fingers from the RF shield lid onto the
7360/8360 TEDand7501/8501 CPUwith dried white paste. Over time those tabs lose tension and trap heat instead of dissipating it! - Proper Thermal Upgrade: Clean both chips with 99% IPA and bond a 40-pin aluminium/copper finned heatsink onto the
7501/8501 CPUand a 48-pin heatsink onto the7360/8360 TEDusing 3M 8810 thermal transfer tape (leave the top tin RF cover off so heat escapes through the case vents!). - HMOS-1 (
7501/7360) vs HMOS-2 (8501/8360): Earlier7501CPUs and7360TEDs use HMOS-1 silicon and run ~10 °C hotter (and fail far more often) than later HMOS-28501R1/8501R4and8360R2chips.
2 Joystick & Cassette Port ESD Danger!
- Why Plugging in a Joystick Kills TED (
7360/8360): Unlike the C64 (where joysticks connect to a replaceable 6526 CIA), on the C16 and Plus/4 the two 8-pin Mini-DIN joystick ports connect straight into the keyboard/data lines (D0–D3, D6, D7) of the 48-pin TED chip! - NEVER plug or unplug a joystick or Mini-DIN-to-DB9 adapter while the computer is switched ON! Even a tiny static spark from your fingers into the joystick plug blows the internal input MOSFETs inside the TED chip!
- Preventative Diode Array Mod: Solder low-capacitance
1N4148orBAT85clamping diodes (orSRV05-4ESD protection arrays) from the joystick data/select lines to+5VandGNDon the underside of the PCB to protect your TED chip permanently.
3 Dead 7501/8501 CPU? Use a 6502 Adapter!
- Original NOS
7501and8501CPUs are rare and expensive because millions failed in the 1980s. - Modern Solution (
6502/6510→7501/8501Replacement Board): Open-source drop-in adapter PCBs (such as the SukkoPera / kinziMOS8501-to-6502or6510adapter) combine a standard, cheap MOS 6502B (2 MHz) (or6510) with a small CPLD/GAL + 74HCT244 to recreate the 7-bit I/O port ($00/$01) andAECtri-state bus control — running stone-cold with 100% software compatibility!
Commodore 264 / TED Family Model Selector
Toggle between the flagship Plus/4 (64KB + 3-Plus-1 suite), the breadbin Commodore 16 (16KB → 64KB upgrade), and the compact C116.
Commodore Plus/4 1984–1986 • ASSY 310163 • 64 KB RAM • 121 Colours
Originally conceived as the "264" business/productivity machine, the dark-charcoal Commodore Plus/4 features a slim sculpted case with a diamond-arranged 4-way cursor rocker, 64 KB of RAM (60671 BYTES FREE in BASIC 3.5!), a 121-colour palette (15 hues × 8 luminance levels + black), built-in Machine Language Monitor (MONITOR), and the built-in 32 KB "3-Plus-1" productivity ROM suite (Word Processor, Spreadsheet, Database, and Graphing) launched by pressing F1 at power-up!
Key ICs & Board Designators (ASSY 310163)
- U2 (CPU): MOS 7501 / 8501R1 / 8501R4 @ 0.89 MHz (active scanline) / 1.77 MHz (border/blanking & screen-off fast mode!)
- U1 (TED): MOS 7360 / 8360R2 (48-pin DIP) — 40×25 text & 320×200 hi-res graphics (121 colours, no hardware sprites!), 3× 16-bit timers, 2-voice square/noise audio, DRAM refresh & keyboard/joystick input
- U19 (PLA): MOS 251641-02 (
FPLA, 28-pin DIP) — memory & chip-select address decoder - U3 (ACIA): MOS / Rockwell 6551AP (28-pin DIP) — hardware RS-232 / Modem UART on the User Port (
1.8432MHzcrystalY2) - U5 (Keyboard Latch) & U27 (User Port PIO): 2× MOS 6529B (20-pin DIP) Single Port Interfaces
- U11–U18 (64KB RAM): 8× 4164 (64K×1, +5 V single-rail) DRAMs
- U23, U24, U25, U26 (4× 28-Pin ROM Sockets):
U23= 16 KB BASIC 3.5 (318006-01),U24= 16 KB Kernal (318004-05PAL /318005-05NTSC),U25= 16 KB 3-Plus-1 Low (317053-01),U26= 16 KB 3-Plus-1 High (317054-01)
Why the Plus/4's 121-Colour Palette & BASIC 3.5 Shine
| Feature | Commodore 64 | Commodore Plus/4 |
|---|---|---|
| Colour Palette | 16 fixed colours | 121 colours (15 hues × 8 brightness levels + black!) |
| Free BASIC RAM | 38,911 Bytes Free | 60,671 Bytes Free (automatic ROM banking!) |
| BASIC Version | BASIC 2.0 (No graphics/sound commands) | BASIC 3.5 (GRAPHIC, CIRCLE, BOX, DRAW, PAINT, SOUND, VOL, DO/LOOP, RENUMBER, MONITOR) |
| CPU Clock Speed | 0.985 MHz (PAL) / 1.023 MHz (NTSC) | 1.77 MHz during VBlank/borders (and POKE 65286,PEEK(65286) AND 239 screen-blank turbo!) |
Plus/4 Diamond Cursor Key Repair: The Plus/4 keyboard uses Mitsumi hybrid plungers over a PCB with conductive carbon-rubber pills. If the 4-way diamond cursor rocker feels mushy or unresponsive, unscrew the keyboard PCB from the back and clean the black carbon contact pads on a sheet of plain white paper + 99% IPA.
Commodore 16 1984 • ASSY 250443 • Charcoal Breadbin • 16 KB Stock RAM
Housed in a dark-charcoal C64/VIC-20 "breadbin" case with light-grey keys, the Commodore 16 was designed to replace the VIC-20 as an entry-level home computer. Internally, its spacious motherboard (ASSY 250443) omits the Plus/4's 6551 ACIA, User Port, and 3-Plus-1 ROMs, powers everything from an external 9 V DC Centre-Negative wall wart via an internal 7805 regulator, and ships with 16 KB of RAM (12277 BYTES FREE) using two 18-pin 4416 (16K×4) DRAMs (U5 & U6).
Key ICs on ASSY 250443 (C16)
- U2 (CPU): MOS 7501 / 8501
- U1 (TED): MOS 7360 / 8360
- U16 (PLA): MOS 251641-02 (28-pin DIP)
- U11 (Keyboard Latch): MOS 6529B (20-pin DIP)
- U3 (BASIC 3.5 ROM) & U4 (Kernal ROM): Two 16 KB 28-pin mask ROMs
- U5 & U6 (RAM): 2× 4416 (16K×4, DIP-18) DRAMs (upgradeable to 2×
4464for 64 KB!) - VR1 (+5V Regulator): 7805 (TO-220) + 5 W cement drop resistor (
R10)
Easy 2-Chip C16 16KB → 64KB RAM Upgrade (4416 → 4464)
Upgrading a 16 KB Commodore 16 to a full 64 KB (60671 BYTES FREE) so it runs 100% of Plus/4 games and demos takes just two chips and two jumper traces:
- Desolder the two 18-pin
4416(16K×4) DRAMs atU5andU6, solder in two 18-pin IC sockets, and insert two4464(64K×4, 100ns–120ns) DRAMs! - On a 16 KB C16, address lines
A14andA15to the74LS257multiplexers (U7&U8) are tied to+5Vso the 16 KB RAM mirrors four times across the 64 KB space. - Cut the two small
+5Vtie tracks onU7Pin 14 andU8Pin 14 (or lift those two pins) and solder two jumper wires from CPUA14(U2 Pin 20) and CPUA15(U2 Pin 21) to the multiplexer inputs! Power on to see60671 BYTES FREE!
Commodore 116 1984 • ASSY 250413 • European Rubber-Key Ultra-Compact
Sold almost exclusively in Germany and Europe, the Commodore 116 is the closest machine to Jack Tramiel's original $49 ZX Spectrum-competitor vision: it packs the exact same electronics as the Commodore 16 (16KB RAM, 7501/8501, 7360/8360 TED, BASIC 3.5) into a tiny dark-grey case half the size of a C16 with a conductive-rubber chiclet keyboard.
C116 Bench & Upgrade Notes
- Same 16KB → 64KB Upgrade as the C16: Uses two 18-pin
4416DRAMs (U5&U6) that can be swapped directly for two4464(64K×4) DRAMs with twoA14/A15wires! - Rubber Keyboard Mat Care: The black conductive carbon dots on the underside of the C116's rubber keymat pick up skin oils and dust over time. Wash the rubber mat in warm soapy water, dry thoroughly, and wipe the gold/copper comb fingers on the keyboard sub-PCB with 99% IPA.
- Cramped Thermal Envelope: Because the C116 shell is much shallower than the C16 breadbin, replacing the internal linear
7805regulator with a 1.5 A switching buck regulator (Recom R-78B5.0-1.5/Traco TSR 1-2450) and adding low-profile copper heatsinks to the CPU and TED is mandatory!
Plus/4 vs C16 vs C116 Hardware Comparison
| Feature | Plus/4 | Commodore 16 | Commodore 116 |
|---|---|---|---|
| Stock RAM | 64 KB (8× 4164) | 16 KB (2× 4416) | 16 KB (2× 4416) |
| 3-Plus-1 ROMs | Yes (U25 & U26) | No | No |
| 6551 ACIA & User Port | Yes (U3 + 24-pin Edge) | No | No |
| Power Connector | 4-Pin Square DIN (or 7-Pin DIN) | Barrel Jack (9V DC Centre-Neg!) | Barrel Jack (9V DC Centre-Neg!) |
Diagnostic Checklist: Black Screen, PLA & DRAM Faults
Isolating dead 7501/8501 CPUs vs 7360/8360 TED chips, testing the 251641-02 PLA, and decoding 4164/4416 RAM corruption.
"Black Screen / No Boot" Decision Tree (CPU vs TED vs PLA)
Power LED lights up, +5 V rail is clean (4.95–5.10V), but screen is completely black (with or without TV sync).
- Step 1 — Check If TV Sync / Dark Raster Is Present on Pin 4 (Composite) / Pin 1 (Luma):
- On the TED series, the 17.734 MHz (PAL) / 14.318 MHz (NTSC) crystal feeds directly into the 7360/8360 TED (
Pin 6), and the TED divides that down to outputΦ0CPU clock (TED Pin 12→CPU Pin 1)! - Probe
CPU Pin 1 (Φ0): if there is NO clock leaving TED Pin 12 (and the crystal is oscillating), the TED chip (U1) or its socket is dead!
- On the TED series, the 17.734 MHz (PAL) / 14.318 MHz (NTSC) crystal feeds directly into the 7360/8360 TED (
- Step 2 — Clock Present at CPU Pin 1, Still Black Screen:
- Check
CPU Pin 13 (/RES)(must go low for ~250 ms then rise to +5 V) andCPU Pin 5 (AEC)(Address Enable Control from TED). - If
/RES,Φ0, andAECare all valid, yet the address lines (A0–A15) are stuck high/low with no activity, your7501/8501 CPU(U2) has died! (Confirm by plugging in a known-good 8501 or a 6502 adapter board).
- Check
- Step 3 — Check the 28-Pin PLA (
251641-02—U19on Plus/4,U16on C16):- A dead
251641-02PLA fails to assert/CS0(BASIC ROM),/CS1(Kernal ROM), or/RAS//CASenable signals, resulting in a black screen with valid sync! - Modern cool-running replacements (such as PLAnktonTED / GAL20V8 PLA adapter) drop straight into the 28-pin PLA socket.
- A dead
- Step 4 — Hold the STOP (or RUN/STOP) Key While Pressing Reset:
- Just like the C128, holding RUN/STOP during reset forces the TED Kernal ROM to jump straight into the built-in TEDMON Machine Language Monitor (
B*) without initializing BASIC 3.5! If the Monitor appears on screen, your CPU, TED, PLA, and Kernal ROM are working, and only the BASIC ROM (U23/U3) or upper RAM is faulty!
- Just like the C128, holding RUN/STOP during reset forces the TED Kernal ROM to jump straight into the built-in TEDMON Machine Language Monitor (
Plus/4 4164 DRAM Bit Map & TED Audio Troubleshooting
Garbled characters on the white/lavender startup screen, wrong BYTES FREE count, or missing/distorted TED sound.
Plus/4 (ASSY 310163) 8-Chip 4164 DRAM Bit-to-IC Map
| Data Bit | Plus/4 DRAM IC | Data Bit | Plus/4 DRAM IC |
|---|---|---|---|
| Bit 0 (D0) | U18 (!/A↔@) | Bit 4 (D4) | U14 (0/Hue bit 0) |
| Bit 1 (D1) | U17 ("/A↔C) | Bit 5 (D5) | U13 (Case/Luminance) |
| Bit 2 (D2) | U16 ($/A↔E) | Bit 6 (D6) | U12 (Luminance/Blink) |
| Bit 3 (D3) | U15 ((/Hue bit 3) | Bit 7 (D7) | U11 (Inverse video block) |
On the C16 / C116: U5 (4416/4464) handles the Low Nibble (D0–D3) and U6 (4416/4464) handles the High Nibble (D4–D7)!
TED Sound Generator (Pin 21 SND) Troubleshooting
- The TED chip includes a 2-channel square-wave + white-noise generator output on TED Pin 21 (
SND). Test in BASIC 3.5 with:VOL 8 : SOUND 1, 500, 60 - If video and keyboard work fine on your TED chip, but audio is completely dead or heavily distorted, trace TED Pin 21 through the external RC low-pass filter and coupling capacitor (
C20/C51) to 8-pin Audio/Video DIN Pin 3 before condemning the TED chip!
Power Supply Pinouts (C16 Polarity Trap & Plus/4 Square DIN) & 8-Pin S-Video
Preventing reverse-polarity damage on the C16/C116, wiring a modern PSU to the Plus/4's 4-pin Square DIN, and connecting S-Video upscalers.
C16 / C116 vs. Plus/4 Power Supply Pinouts CRITICAL POLARITY WARNING!
DANGER — C16 & C116 Barrel Jack Is 9V DC CENTRE-NEGATIVE! Unlike almost all modern electronics, the Commodore 16 and C116 use a 9 V DC (1.0 A) CENTRE-NEGATIVE barrel plug (Outer Barrel = +9V, Inner Tip = GND, same polarity as a ZX Spectrum or guitar pedal)! Although Commodore fitted a small reverse-protection diode (CR1 1N4001) before the internal 7805, if CR1 fails open or a high-current centre-positive brick is connected, the regulator can be damaged.
| Machine | Power Socket Type | Pinout & Voltage Specification |
|---|---|---|
| Commodore 16 & C116 | 5.5 mm × 2.1 mm Barrel Jack | 9.0 V DC @ 1.0–1.5 A • CENTRE-NEGATIVE! (• Inner Tip = GND (0 V) • Outer Barrel = +9 V DC). Feeds internal 7805 (+5 V) + 5 W drop resistor R10. |
| Commodore Plus/4 (Most Models — Square DIN) |
4-Pin Square DIN Power (Viewed looking into male PSU plug) |
• Pin 1 (Top-Left): +5.0V DC Regulated (@ 1.5–2.0 A)• Pin 2 (Bottom-Left): GND (0V) Digital Return• Pin 3 (Top-Right): 9.0V AC (Line 1 @ 1.0 A)• Pin 4 (Bottom-Right): 9.0V AC (Line 2 Return) |
| Early Commodore Plus/4 (7-Pin Round DIN) |
7-Pin Circular DIN (Same as C64!) | Identical pinout and voltages to the Commodore 64 (Pins 1–3 = GND, Pin 5 = +5V DC, Pins 6–7 = 9V AC). Use a modern C64 saver/replacement PSU! |
Note on Plus/4 vs C128 Square DIN Plugs: The Plus/4 uses a 4-pin Square DIN (no center pin), whereas the Flat C128 uses a 5-pin Square DIN (with a center pin)! You can easily build a C64-to-Plus/4 power adapter cable to run your Plus/4 from any modern C64 power supply.
8-Pin DIN Audio/Video Port 262° Horseshoe • C64 S-Video Compatible!
All three TED machines (Plus/4, C16, and C116) share the exact same 8-pin 262° horseshoe DIN A/V pinout as the Commodore 64 and C128! Because the 7360/8360 TED outputs separated Luminance (Pin 1) and Chrominance (Pin 6) with zero vertical jailbars, the Plus/4 and C16 produce one of the cleanest S-Video pictures of any 8-bit computer:
| DIN-8 Pin | TED Series Signal | RCA / S-Video / Upscaler Target |
|---|---|---|
| Pin 1 | Luminance + Sync (Y) | S-Video Y (Pin 3) — razor-sharp luma! |
| Pin 2 | GND (0 V Shield) | Video & Audio Ground |
| Pin 3 | Audio Out (Mono) | White / Red RCA Audio (from TED Pin 21) |
| Pin 4 | Composite Video (CVBS) | Yellow RCA Composite Video |
| Pin 5 | Audio In | External audio mix input |
| Pin 6 | Chrominance (C) | S-Video C (Pin 4) via 300 Ω series resistor! |
| Pin 7, 8 | NC | Leave unconnected |
Why a 300 Ω Series Resistor on Chroma (Pin 6) Is Recommended: Just like the C64, the TED's Chroma output is slightly hotter than modern 75 Ω S-Video inputs expect. Adding a 300 Ω resistor in series inside the S-Video plug eliminates colour checkerboard patterning on RetroTINK / LCD displays.
Mini-DIN Joystick (Joy 1/2), Mini-DIN Cassette & 50-Pin Cartridge Bus
Adapter wiring to use standard 9-pin Atari/C64 joysticks and C2N Datasettes on the C16, C116, and Plus/4.
8-Pin Mini-DIN Joystick Ports (JOY 1 & JOY 2) to Standard DB9 Adapter
See also our dedicated Plus/4 4-Pin Square DIN & C16 9V Centre-Negative Power, 8-Pin DIN A/V, and 6-Pin IEC Serial pages. To save board space on the C116, Commodore replaced the standard 9-pin D-Sub joystick ports with 8-pin circular Mini-DIN sockets! Note that TED joysticks are active-low matrix-strobed (the fire/direction switches connect to Select strobe Pin 5, NOT directly to ground, though passive Mini-DIN-to-DB9 adapters tie DB9 Pin 8 to Mini-DIN Pin 5 Select):
| Mini-DIN 8 Pin | TED Signal | Standard Atari / C64 DB9 Male Pin |
|---|---|---|
| Pin 1 | UP (D0 / K0) | DB9 Pin 1 (Up) |
| Pin 2 | DOWN (D1 / K1) | DB9 Pin 2 (Down) |
| Pin 3 | LEFT (D2 / K2) | DB9 Pin 3 (Left) |
| Pin 4 | RIGHT (D3 / K3) | DB9 Pin 4 (Right) |
| Pin 5 | /JOY SELECT Strobe (D2 on Joy 1 / D1 on Joy 2) | DB9 Pin 8 (Common Return!) — Connect DB9 Pin 8 here, NOT to Pin 8 GND, or the joystick will ghost onto the keyboard! |
| Pin 6 | /FIRE (D6 on Joy 1 / D7 on Joy 2) | DB9 Pin 6 (Fire Button) |
| Pin 7 | +5 V DC (Autofire Power) | DB9 Pin 7 (+5 V — optional) |
| Pin 8 | GND (0 V Shield) | Used ONLY for autofire ground (Do NOT tie DB9 Pin 8 here!) |
CRITICAL ADAPTER WIRING DETAIL: On a passive C16/Plus/4-to-DB9 joystick adapter, DB9 Pin 8 (Common) MUST connect to Mini-DIN Pin 5 (/JOY SELECT) — if a poorly made adapter ties DB9 Pin 8 to Mini-DIN Pin 8 (GND), every time you push the joystick you will type random letters across the screen because the joystick lines are shared with the keyboard matrix!
7-Pin Mini-DIN Cassette Port (1531 Datasette) to C64 6-Pin Edge
The black Commodore 1531 Datasette is electrically identical to a standard C64/VIC-20 1530 C2N Datasette — only the plug was changed to a 7-pin Mini-DIN:
| Mini-DIN 7 Pin | Signal | C64 Datasette Edge Finger |
|---|---|---|
| Pin 1 | GND (0 V) | Pin A / 1 (GND) |
| Pin 2 | +5 V DC (Logic Power) | Pin B / 2 (+5 V) |
| Pin 3 | +6 V Motor Supply | Pin C / 3 (Cassette Motor) |
| Pin 4 | READ (Data In to CPU Port Bit 4) | Pin D / 4 (Read) |
| Pin 5 | WRITE (Data Out from CPU Port Bit 0) | Pin E / 5 (Write) |
| Pin 6 | SENSE (Key Pressed Sense to CPU Port Bit 2) | Pin F / 6 (Sense) |
| Pin 7 | NC / Shield | — |
50-Pin Rear Cartridge Expansion Slot & IEC Serial
The 50-pin (2×25, 0.1″ pitch) rear Cartridge Slot exposes the full 7501/8501 address and data bus plus /CS0 (Low ROM $8000–$BFFF), /CS1 (High ROM $C000–$FDFF), /C1LOW//C1HIGH external cartridge ROM banking, and the hardware DMA bus used by the high-speed Commodore 1551 Parallel Floppy Drive! Meanwhile, the standard 6-pin DIN IEC Serial Port works directly with all 1541, 1571, SD2IEC, and Pi1541 drives!
Chip & 28-Pin JEDEC ROM / EPROM Reference
Interactive IC Pinout Finder cards plus TED custom silicon and 27C128 / 27C256 ROM upgrades.
MOS 7501 / 8501 CPU
U2 — 6502-core microprocessor with a 7-bit built-in I/O port ($00/$01 for cassette/IEC) and AEC bus-enable pin (no /NMI).
MOS 7360 / 8360 TED
U1 — Text Editing Device: 121-colour video, 2-voice sound, 3 timers, DRAM refresh, and keyboard/joystick latch.
View Pinout →MOS 6502B (Adapter CPU)
Used on modern 6502-to-8501 replacement adapter boards to replace failed 7501/8501 CPUs.
4416 & 4464 DRAM
U5 & U6 (C16 & C116) — 18-pin nibble-wide DRAMs (upgrade 2× 4416 to 2× 4464 for 64 KB!).
View Pinout →4164 DRAM (×8)
U11–U18 (Plus/4) — Eight single-rail +5 V 64K×1 dynamic RAM chips providing 64 KB.
View Pinout →TED Series Custom Silicon Reference
| Chip | Part Numbers | Function & Modern Replacements |
|---|---|---|
| TED (U1) | MOS 7360R7 (HMOS-1) MOS 8360R1 / 8360R2 (HMOS-2) |
48-pin DIP Text Editing Device ($FF00–$FF3F). Note: PAL vs NTSC is selected by a motherboard jumper (J1) and crystal (17.734MHz PAL vs 14.318MHz NTSC) — every 7360/8360 TED chip supports BOTH PAL and NTSC on the same die! FPGA replacement: FPGA-TED / LittleSixteen. |
| CPU (U2) | MOS 7501 (HMOS-1) MOS 8501R1 / 8501R4 (HMOS-2) |
40-pin DIP CPU. Replace with an HMOS-2 8501R4 or a cool-running 6502/6510-to-8501 adapter board. |
PLA (U19 / U16) |
MOS 251641-02 (DIP-28) | 28-pin Programmable Logic Array. Replaceable with a PLAnktonTED or programmed GAL20V8 adapter. |
SPI (U5 / U27) |
MOS 6529B (DIP-20) | 8-bit Single Port Interface latching the keyboard matrix rows (and parallel User Port data on Plus/4). |
ACIA (U3 Plus/4) |
MOS / Rockwell 6551AP (DIP-28) | Hardware UART mapped at $FD00–$FD03 for RS-232 / User Port serial communications. |
28-Pin JEDEC ROM Sockets (27C128 / 27C256 Drop-In!)
Every 16 KB ROM socket in the Plus/4, C16, and C116 uses a standard 28-pin JEDEC pinout — meaning standard 27C128 (16 KB) UV EPROMs plug straight in with zero adapters!
| ROM Function | Plus/4 Socket | C16 / C116 Socket | Commodore Part # & EPROM Upgrade |
|---|---|---|---|
BASIC 3.5 (16KB)( $8000–$BFFF) |
U23 |
U3 |
318006-01 — Direct drop-in: 27C128 (16 KB) (or 27C256 with upper/lower 16K duplicated). |
Kernal OS (16KB)( $C000–$FFFF) |
U24 |
U4 |
318004-05 (PAL Rev 5) / 318005-05 (NTSC Rev 5). Direct drop-in: 27C128 (or 27C256 Dual-Kernal switcher with JiffyDOS Plus/4 for fast SD2IEC/1541 loading!). |
3-Plus-1 Suite Low & High (2×16KB) |
U25 (Low)U26 (High) |
Not Present (Can be loaded from cart!) |
317053-01 & 317054-01. Can be replaced with custom Internal Function ROMs (27C128/27C256) containing Diagnostic ROMs, Turbo Plus, or game menus! |
Resources & Further Reading
Blog posts, interactive bench tools, and essential Commodore Plus/4 & C16 communities.
Smiggy's Commodore Posts
Bench Tools & Machine Hubs
- Retro File Utilities (Rust/Wasm) —
.D64disk parser, 6502/7501/8501 disassembler & 27C128 ROM.BINpatcher - IC Pinout Finder — 7501/8501, 6502, 4164 & more
- Connector Pinout Directory — Plus/4 4-Pin Square DIN & C16 Power, Mini-DIN Joystick & 1531 Tape, 8-Pin DIN S-Video, IEC Serial
- Recap & Repair Reference — capacitor replacement guide
- Ohm's Law Calculator
- C64 Machine Hub — Commodore 64 reference
- VIC-20 Machine Hub — Commodore VIC-20 reference
- Commodore PET Hub — PET 2001, 4000 & 8000 reference
- C128 Machine Hub — C128, C128D & DCR reference
- SX-64 Machine Hub — Executive Portable C64 reference
- Amiga Machine Hub — A500/A600/A1200 reference
- Big-Box Amiga Hub — A1000, A2000, A3000 & A4000 reference
- Atari ST Hub — 520ST, 1040STFM & STE reference
- Atari 8-Bit Hub — 400/800, 800XL & 130XE reference
- Apple IIe Hub — Unenhanced, Enhanced & Platinum reference
- BBC Micro Hub — Model B, B+ & Master 128 reference
- Acorn Atom & Electron Hub — Atom & Electron reference
- ZX Spectrum Hub — 16K/48K & +2/+3 reference
- Sinclair QL Hub — 68008, Microdrive & ULA reference
- Dragon 32/64 Hub — Dragon 32 & 64 reference
- Oric-1 & Atmos Hub — Oric 6502A & ULA reference
- Amstrad CPC 464 Hub — CPC 464 & Datacorder reference
- Amstrad CPC 6128 Hub — 128K & 3″ disc reference
- MSX Machine Hub — MSX1, MSX2, MSX2+ & Turbo R reference
- Osborne 1 & Kaypro II Hub — CP/M luggable reference
- TRS-80 & CoCo Hub — Model I/III/4 & CoCo 1/2/3 reference
- TI-99/4A Machine Hub — 16-bit TMS9900 & PEB reference
External Plus/4 & C16 Resources
- Plus/4 World — the definitive Commodore Plus/4, C16 & C116 software, hardware, and forum encyclopaedia
- Zimmers.net TED Series Schematics — official Commodore C16, C116, and Plus/4 service manuals
- Ray Carlsen's Plus/4 & C16 Repair Guides — chip-by-chip fault symptoms and PSU notes
- Open-Source C16/Plus/4 Hardware Projects — 64K RAM expansions, 8501 CPU adapters, and cartridge PCBs
Plus/4 & C16 (TED) — Capacitor & Recap Reference
Board revisions, electrolytic capacitor lists, voltage/farad ratings, and Through-Hole servicing notes.
Commodore Plus/4 & C16 (TED) — Plus/4 ASSY 310163 & C16 ASSY 250443
Commodore 264 Series TED mainboards • Mount: Through-hole • Difficulty: Beginner friendly
Commodore Plus/4 Mainboard (ASSY 310163) (6 Capacitors)
| Ref | Capacitance | Voltage | Package / Type | Circuit Location & Bench Notes |
|---|---|---|---|---|
C2 |
10 uF | 25 V | Radial | |
C11 |
10 uF | 25 V | Radial | |
C20 |
470 uF | 16 V | Radial | |
C50 |
2200 uF | 16 V | Axial | |
C51 |
100 uF | 16 V | Radial | |
C52 |
470 uF | 16 V | Radial |
Commodore 16 Mainboard (ASSY 250443) (5 Capacitors)
| Ref | Capacitance | Voltage | Package / Type | Circuit Location & Bench Notes |
|---|---|---|---|---|
C10 |
2200 uF | 25 V | Axial | |
C11 |
470 uF | 16 V | Radial | |
C14 |
10 uF | 25 V | Radial | |
C25 |
10 uF | 25 V | Radial | |
C41 |
220 uF | 16 V | Radial |
Complete Diagnostic Flowchart: Capacitive Load, ESR & Power Rail Ripple Diagnostic Tree (Universal Retro Mainboards (C64, Amiga, ZX Spectrum, Game Gear, Consoles))
Plus/4 & C16 (TED) — System Bench Tools & IC Pinouts
Click any chip below to open its interactive DIP/PLCC pinout diagram, pin-by-pin signal table, and oscilloscope test waveforms.
MOS 6502
MOS 6502 / R6502 / UM6502
The 8-bit CPU at the heart of the Apple II, PET, VIC-20, BBC Micro and Atari 2600.
Open Interactive Pinout →MOS 7501 / 8501
MOS 7501 / 8501
The Commodore 16 and Plus/4 CPU — a 6502 core with a 7-bit I/O port, no /NMI and no PHI2 output.
Open Interactive Pinout →MOS 7360 / 8360 TED
MOS 7360 / 8360R2 (Text Editing Device)
The single-chip heart of the Commodore 16, C116 and Plus/4 — 121-colour video, 2-channel sound, 3 timers, DRAM refresh and unbuffered joystick/keyboard latch.
Open Interactive Pinout →4164 64K x 1 DRAM
4164 / MT4264 / TMS4164 / MB8264 / KM4164 / 41464 (x4)
64K x 1 DRAM, single +5 V. VCC is pin 8 and GND is pin 16 — the reverse of almost every other 16-pin DIP. Apply 5 V to pin 16 and it dies.
Open Interactive Pinout →4416 / 4464 (16K/64K x 4) DRAM
TMS4416 / MB81416 / TMS4464 / MT4067 / KM41464
The 18-pin nibble-wide (x4) DRAM family — just TWO chips replace eight 4116/4164 DRAMs! Upgrading 4416 to 4464 unlocks 64KB on the C16, C128 VDC, CoCo 2 and Atari 600XL.
Open Interactive Pinout →Signal & Trace Visualizer (Scope)
Compare healthy vs. faulty CPU clocks, reset ramps, PLA strobes, and 5V PSU ripple waveforms.
Disassembler & ROM LabRetro File Utilities (Rust/Wasm)
6502/6510 disassembler with IC register links, C64 .D64 parser, and EPROM CRC32 verifier/patcher.
Logic & PinoutsConnector & Port Pinout Reference
59 interactive RGB SCART, DIN A/V, PSU polarity, joystick, floppy, and expansion bus pinouts.
Logic & PinoutsLogic & RAM Substitution Guide
Cross-reference 4116→4164 DRAM mods, 2364→27C256 EPROM adapters, and 74LS/74HCT swaps.