Commodore Plus/4 upgrades

Replaces the CPU in Commodore 264-series computers and can add 512 KB of Hannes-compatible expanded memory.

For this system (exact model): The seller explicitly names the Plus/4. The 512 KB path requires removal of the original DRAM and Hannes-compatible software support.

Lotharek marks the module discontinued. CPU-only use requires correct pin-1 orientation and a compatible socket or safe desoldering. Enabling the 512 KB expansion is invasive: remove the original DRAM and connect CAS to pin 15 on an eight-chip, 1-bit layout or pin 16 on a two-chip, 4-bit layout. Confirm the exact motherboard, CPU package, memory layout, and software's Hannes banking support before buying or installing a used module.

Current composite and S-Video cable options for compatible Commodore computers, with a five-pin composite branch that also serves selected Atari systems.

For this system (exact model): The seller explicitly lists the Plus/4 for both the five-pin composite family and the eight-pin S-Video and composite cable. The stock audio source is mono even when a cable provides two audio connectors.

The two five-pin products exposed Add to cart controls, while the eight-pin product exposed current priced options on 2026-07-30. The five-pin cable and adapter carry composite video and two audio connectors; those connectors do not create an independent stereo source in a stock mono computer. The eight-pin S-Video branch requires a host that supplies separate luma and chroma. Its stereo option requires a compatible second audio source on the designated extra pin. Match the connector, resistor, audio wiring, display input, and regional video standard before ordering.

A current 1.5-meter five-pin DIN to SCART cable for several Commodore computer families.

For this system (exact model): The seller explicitly lists the Plus/4. This is a composite-video cable for a display with a compatible SCART input.

The product page exposed a current Add to Cart path on 2026-07-30. The cable is 1.5 meters long and terminates in a five-pin DIN plug, so it does not carry the separate luma and chroma signals used for S-Video. Confirm that the intended display accepts composite video through SCART and that its regional video standard matches the computer.

Uses one microSD cartridge and interchangeable adapters to load software and provide selected storage, cartridge, memory, and diagnostic functions on many vintage computers.

For this system (exact model): Use the Commodore 16/Plus/4 adapter. The current product page lists BBT, BIN, CRT, D64, D71, D81, D8B, P00, PRG, and T64 support for this platform.

The current store listed the assembled BackBit Pro for $129 on 2026-07-27 with one assembled adapter choice included. A microSD card is not included. Additional adapters are sold separately and require through-hole soldering. Firmware updates use the microSD card. An original C64 Assy 326298 needs the documented reset fix, and the SX-64 needs the straight C64/128 adapter.

Adds SD-card PRG and TAP loading, a fast loader, Wi-Fi file transfer, and cross-development tools through the cassette port of several Commodore 8-bit families.

For this system (exact model): The maker reports successful Plus/4 testing. Some programs that overwrite the cassette buffer may need the standard slow PRG loader. Disable JiffyDOS and avoid other cassette-port hardware.

The maker states that Cassiopei v2.0 is not available. The hardware is described as functionally complete, while firmware, software, manuals, and downloadable updates remain published.

Licensed, made-to-order recreation of the CMD hard drive with BlueSCSI v2 and externally accessible SD storage.

For this system (exact model): The seller explicitly lists the Plus/4. Confirm that the intended software supports the drive's DOS and partition features.

ToTs RETRO exposed an Add to Cart path at USD 899.99 on 2026-07-27. Each drive is made to order with an advertised lead time of up to one week. Supply an IEC serial cable and a compatible 1581 or 1541-II power supply; neither is included. The seller has not tested simultaneous tape-drive use.

External displays for checking the 5 VDC and 9 VAC outputs of Commodore power supplies, with the MkII adding current measurement under load.

For this system (exact model): The review reports seller-stated Plus/4 support but does not test it or identify the required cable, connector, or reset wiring. Do not improvise an adapter from the C64 or VIC-20 setup.

The exact review was published in March 2020 and a February 2023 comment says the seller was still making the monitors. The review describes an unofficial Commodore-styled product made by an unnamed Australian builder, not a verified Commodore-manufactured accessory. A current-looking Pocket 1501 eBay route failed exact Tavily extraction and failed again after the required 60-second retry under WF-068, so its maker, stock, price, package, and relationship to MkI and MkII remain unverified. The separate FDD II drive-supply monitor is not folded into this host-monitor family. This device displays readings; no automatic cutoff, regulation, over-voltage clamp, fuse, or other protective action was verified.

6522 VIA interposer that changes a Commodore 1541 drive between device IDs 8 through 11 without cutting its original jumpers.

For this system (bus/interface): Use through a compatible 1541 drive. External DIP-switch wiring is optional and may require modifying the drive case.

TheRetroChannel listed five boards in stock on Lectronz on 2026-07-27. External wiring and DIP switches are not included. A drive with a soldered 6522 first needs the chip desoldered and a socket installed; an external switch may require case cutting.

Host-specific passive A/V adapters for the VIC-20, C128 family, Plus/4, and Ultimate64 replacement mainboards.

For this system (exact model): The Plus/4 variant provides composite, S-Video, and the machine's mono audio duplicated to left and right outputs. Its bypassable 330-ohm resistor controls chroma attenuation; the two audio jacks are not true stereo.

Commodore4ever exposed active Add to cart controls for all four variants on 2026-07-30. The Ultimate64 board uses a different A/V pinout from an original C64; do not use that adapter on a stock C64 or assume compatibility with the newer Commodore 64 Ultimate. The C128 variant handles the 40-column analog output, not the separate 80-column RGBI port.

Protected switched-mode replacement supplies for the C64 and round-connector VIC-20CR, with separate adapters for the C128 and Plus/4.

For this system (exact model): Use only Commodore4ever's dedicated 64-to-Plus/4 adapter with an ATOM, PS-64, or PS-64/128 supply. The seller explicitly declines to guarantee or endorse the adapter with another brand. The adapter was sold out on 2026-07-30.

On 2026-07-30, Commodore4ever listed the original ATOM and ATOM v2.5 at USD 59.99 and ATOM RETRO at USD 69.99; all three were sold out. The official Plus/4 adapter was also sold out at USD 24.99. A separate live 90-degree adapter page listed a 64-to-128 option at USD 14.99, but did not expose unambiguous variant stock or identify every supported ATOM revision. The original ATOM page lists separate North American 120 VAC and European 230 VAC configurations, ATOM v2.5 lists only the North American input, and ATOM RETRO says its European version is currently unavailable. Surviving pages provide too little detail to establish exact specifications or final availability for the older PS-64 with LED and PS-64/128. Do not assume that ATOM specifications apply to those predecessor models.

User-port Wi-Fi modem for reaching Telnet BBS services from several Commodore 8-bit computers.

For this system (exact model): The seller lists Plus/4 compatibility but explicitly says it has not been personally tested.

The seller's collection listed the modem as sold out on 2026-07-30. An optional case is an accessory for the same modem family. The product page does not provide a public firmware or complete hardware build package.

DIY diagnostic ROM and loopback harness for PAL and NTSC Commodore 264-family computers.

For this system (exact model): The maker explicitly tested the Plus/4. Add the Plus/4 user-port loopback to exercise the 6529 port and 6551 or 8551 ACIA in addition to the serial and cassette loops. Inserting that edge connector upside down can short 9 VAC to 5 V and damage the computer, so key and label the connector and work only with power off.

Rob Clarke's current download directory offered Diag264 0.97 on 2026-07-30. The maker also offers a programmed EPROM at media and postage cost by email. The software is CC BY-NC-ND 4.0: unmodified personal distribution with attribution is allowed, but modification and commercial resale are prohibited. The maker warns that some third-party marketplace copies were unauthorized or modified. Loopback hardware may be resold when the attribution conditions are met.

Modern VIC-1011-style user-port RS-232 adapter with status lights, reset, and a software-dependent 9600-baud mode.

For this system (exact model): The seller explicitly lists the Plus/4, but does not document which adapter mode and terminal software to use.

Tindie marked the adapter out of stock on 2026-07-30 and says it has been sold out since 2026-01-05. A DB25-to-DB9 adapter is an optional passive accessory, not a separate catalog product.

User-port USB serial adapter for linking supported Commodore 8-bit computers to a modern host's virtual COM port.

For this system (exact model): The seller explicitly lists the Plus/4 as compatible.

The Tindie seller was taking a break on 2026-07-30 and did not expose an ordering path. GGLABS publishes a schematic, but the page does not present a complete fabrication and assembly package.

Licensed replacement computer and disk-drive ROM system that accelerates Commodore serial storage and adds DOS commands.

For this system (exact model): The official site identifies the Plus/4 as a supported computer family. Obtain a licensed, machine-specific offering and verify the exact ROM package and installation method.

The official licensing site listed five authorized sales channels on 2026-07-27. Offerings include licensed ROM images, replacement ROM overlays, and switchless overlays; stock and the exact supported machine or drive vary by seller.

A repairable metal-cased C64 replacement supply with fused 5 VDC and 9 VAC sections, a power switch, and optional C128 or Plus/4 adapters.

For this system (exact model): Plus/4 use requires the separately priced pigtail adapter. Confirm the exact connector and adapter supplied for the computer rather than adapting the C64 lead yourself.

The newest readable announcement was published on April 18, 2022 and listed the Nu-Brick 64 at USD 65 plus USD 15 shipping, with C128 and Plus/4 pigtail adapters at USD 15 each. It directs buyers to message Kevin Ottum on Facebook. No current stock or price page was verified on 2026-07-30, so confirm that he is still accepting orders and specify the required computer and connector.

CPLD replacements for failed PLA chips, currently sold for Commodore 264-series computers and previously made for the C64.

For this system (exact model): The seller explicitly names the Plus/4. Verify the original PLA package, motherboard revision, socket state, and module orientation before fitting it.

The 264-series module exposed a login-or-register-to-buy path on 2026-07-27, while the separate C64 version is discontinued. Human review says the module plugs into the original socket, but the seller does not establish that every supported motherboard is socketed or document the original MOS part, board revisions, orientation, removal, or clearance. Treat it as a plug-in replacement only after confirming a compatible socket and orientation. A used C64 module needs the same checks.

Emulates Commodore IEC devices and loads files from local flash, an SD card, or network servers over Wi-Fi.

For this system (exact model): The project repository explicitly names the Plus/4 and connects through its IEC serial bus. No single retail board is canonical, so match the selected ESP32 hardware profile to its firmware.

The project provides source, several ESP32 hardware profiles, build instructions, and a browser-based firmware flasher. No direct retail source was verified, so builders must select matching hardware and firmware before connecting it to a computer.

Open PCB that exposes every Commodore 1530 Datassette connector line for Tapuino builds and cassette-port adapters.

For this system (exact model): The README gives the same exact 1530-to-seven-pin Mini-DIN adapter method for the Plus/4. This requires a correctly wired user-built cable; the shared PCB order supplies only the board.

The repository provides the KiCad board, schematic, footprint, and documentation files and invites builders to fabricate the open hardware. PCBWay currently offers the 26.92 by 26.03 mm V2 design as a 1.6 mm, two-layer bare PCB and labels that shared project CC BY-SA 3.0. No connector, Mini-DIN lead, enclosure, Tapuino electronics, buffering, isolation, fusing, or current limiting is included or documented. Review the manufacturing files and wiring before ordering and connect hardware only with power off.

Cycle-exact Commodore 1541 disk-drive emulation using a Raspberry Pi and SD-card disk images.

For this system (exact model): The official project explicitly supports the Plus/4 through its IEC serial bus. Supply the required Raspberry Pi, SD card, serial cable, legal drive ROM, and external power.

Retro Electronics listed one assembled Option B Pi1541 Hat in stock on 2026-07-25. The Hat is the only supplied part; add a supported Raspberry Pi, SD card, serial cable, legal drive ROM, quality USB cable, and at least a 2.5 A power supply. The official project does not support Raspberry Pi 4 or 5.

A compact semiconductor protector for the 5 VDC and 9 VAC rails of compatible Commodore power supplies.

For this system (exact model): The seller offers a separately selected Plus/4 version using a modified square five-pin male connector for an additional EUR 8. Order the model-specific version and do not attach the standard C64 seven-pin unit or improvise an adapter.

CMD Marketplace listed four units at USD 40 on 2026-07-30. The page claims a 20 microsecond semiconductor response versus 200 milliseconds for a relay design. After a 5 V trip, its 1.25 A SMD fuse must be replaced with a soldering iron; one spare is supposed to be included. The page simultaneously displayed a USD 9 United States rate and a notice that the item does not ship to the United States, so confirm destination availability before ordering.

Custom replacement supplies ranging from simple C64 units to multi-connector systems for several Commodore computers and drives.

For this system (exact model): The preserved maker description says a custom multi-output system can be built for the Plus/4. This is a made-to-order option rather than evidence that every illustrated C64/128 supply includes the required connector. Confirm the exact output, connector, and simultaneous-load configuration.

The readable C64 OS feature was last modified in September 2022 and gave a USD 35-100 range for standard examples, with more elaborate custom builds possible. It directed orders and inquiries to Ray Carlsen by email. Both linked maker pages failed Tavily extraction and failed again after the required 60-second retry under WF-066 and WF-067, so current ordering, prices, model names, electrical ratings, protection, and mains options must be confirmed directly. Do not transfer the specifications or simultaneous-device behavior of one custom build to another.

Current handmade composite, S-Video, SCART, and luma/chroma cable choices for compatible Commodore computers.

For this system (exact model): The seller explicitly lists the Plus/4 for the composite family. Confirm the machine connector and selected lead before ordering.

AMI64 exposed current priced choices on 2026-07-30. The eight-pin S-Video branch includes a 300-ohm chroma resistor. Connector, signal, and display requirements differ between variants: select a five-pin composite lead for an early C64 or VIC-20, and use the eight-pin luma/chroma branches only with a computer and display that expose those separate signals. The seller describes PAL and NTSC use, but the connected display must still accept the computer's regional video standard.

A historical relay protector with alternate DC and AC inputs for several Commodore power configurations.

For this system (exact model): The maker supports the Plus/4 only through a model-specific adapter. No current adapter source was verified. Do not connect a C64 cable directly or improvise the Plus/4 wiring.

The surviving Round 4 sale thread is explicitly titled SOLD and dates to 2017. It offered complete kits at USD 45 and assembled units at USD 85. C64 OS repeated those prices in 2022, but that does not establish later production. The former hookturn.com user-guide URL now resolves to a parked domain. Use the preserved feature and forum specifications for identification, and search the used market rather than contacting the old seller as though stock were current.

Family of IEC storage devices that lets supported Commodore computers access files and disk images on SD or other removable media.

For this system (exact model): The Endresz hardware guide explicitly lists the Plus/4. Confirm the physical serial connection and power method for the chosen board rather than assuming a C64 cassette-port package will fit.

Retro Lemon listed its user-port-powered C64, C128, VIC-20, and SX-64 variant in stock at GBP 34.17 on 2026-07-27, and Sordan exposed a current Buy now path for its combined SD2IEC and Tapecart variant. PolyPlay's plain external Sordan Micro device and Retro Electronics' internal board were out of stock, while the RetroFletch backplane seller was on a break. A complete open C64 SD2IEC LP hardware build is also available. Variant power, connectors, controls, and firmware configuration differ. The official firmware site says 0.x firmware is obsolete and warns that newer-dated bootloaders are not necessarily safer or better.

Assembly kit that adds a numeric track or sector display to supported Commodore floppy drives.

For this system (bus/interface): Use the display through a supported 1541-family serial drive. The modification is installed inside the drive and needs through-hole assembly and wiring.

Commodore4ever and Protovision both exposed current-priced product pages on 2026-07-27, but neither extraction exposed an unambiguous Add to Cart control. Confirm availability before ordering. The kit requires through-hole assembly, display wiring, and internal drive installation; stacked boards or sockets can create clearance problems.

Uses a Raspberry Pi cartridge to emulate memory, sound, cartridges, ROMs, and file-loading functions across several Commodore 8-bit systems.

For this system (exact model): Sidekick264 requires the passive adapter, a Raspberry Pi 3A+ or 3B+, d=3 delay, some overclocking, and external power. The computer's own reset button must normally be used, and C1-high cartridge emulation needs an additional signal wire.

The open project publishes Gerbers, BOMs, software, and case files for full-size and Zero boards. Retro-Updates' assembled Sidekick64 Zero was out of stock on 2026-07-27 and excludes the Raspberry Pi Zero 2. The maker calls the project a personal playground and warns that unsupported images, timing glitches, and unsafe cartridge combinations remain possible.

Connects a Super Nintendo controller to the user port of supported Commodore computers for software written to read its serial protocol.

For this system (exact model): The seller explicitly names the Plus/4 and says its normal jumper arrangement supplies power. Software must explicitly scan the adapter.

TexElec listed the adapter at USD 14.99 and in stock with backordering enabled on 2026-07-30. Most supported machines use the supplied power jumper. Some PET systems do not provide user-port power and need 5 V from the cassette port or an external source; high-current third-party controllers should also use external power because the user port is rated for 100 mA.

Adds a live track, density, write-protect, motor, and sync display to supported Commodore floppy drives.

For this system (bus/interface): Use through a supported 1541-family serial disk drive. Confirm the drive model, tracker variant, display mounting, and required soldering before installation.

The standard and 6522-included variants were both out of stock on 2026-07-24. The 1541-II and 1571 require the special version with a 6522 VIA soldered to the tracker board; the standard version will not work in those drives. Installation can require desoldering the original VIA, fitting a socket, and mounting the display and button externally.

Installs inside supported Commodore floppy drives to duplicate protected disks and add disk utilities.

For this system (bus/interface): Use through a supported 1541-family serial disk drive. The board modifies the drive rather than the Plus/4, and the correct version depends on the drive model.

Both assembled variants were out of stock on 2026-07-24. Each listing includes a 40-pin socket and version 6.0 software on two 5.25-inch disks. Some drives require desoldering the 6502 and installing a socket, so identify the drive model and board revision before ordering or installing.

Configurable replacement for failed 82S100-based Commodore PLA chips, with documented modes for selected C64, 264-series, PET, CBM-II, and 1551 hardware.

For this system (exact model): Remove all configuration jumpers and use socket U19. Verify the board, original chip, socket, and orientation before installation.

Individual Computers' main product index, last modified in May 2026, lists SuperPLA V4 as a spare part while placing the older SuperPLA and V3 under Sold out. The current shop root also exposes a Super PLA V4 product image, but Tavily did not expose an exact product-specific cart or stock control on 2026-07-30. Confirm current orderability before buying. The underside jumpers and adapter pins are very small; use the official mode diagram, tweezers, bright light, and careful handling.

Arduino-based SD-card datasette emulator family for Commodore cassette ports, with TAP writing on the Mini variant.

For this system (exact model): Both seller variants explicitly support the Plus/4 but require a separate C16/Plus/4 cassette-port adapter. Connect or remove all hardware only while the computer is powered off.

Retro Electronics listed one full-size Tapuino and two Tapuino Mini units in stock on 2026-07-27. An SD card is not included, and the required C16/Plus/4 cassette-port adapter is excluded.

Adds SD mass storage to Commodore 264-series computers and can replace the paddle cartridge in a real 1551 drive.

For this system (exact model): The project explicitly supports the Plus/4. Its patched browser provides the documented faster loading path, and the hardware can also replace a real 1551 paddle cartridge.

The repository provides Gerbers, firmware, hardware instructions, and release files sufficient for a DIY build. The maker invites requests for a completed unit but does not advertise standing stock. Disk images are read-only, and the device does not reproduce a 1551 exactly. When a TCBM cable is fitted, both specified ground pins must be connected as documented.

Connects modern Bluetooth gamepads and, on selected models, mice to Commodore, Amiga, and Atari computers.

For this system (exact model): Eduardo Casino's open TED-series layout explicitly supports the Plus/4. It needs a 1 mm PCB, an ESP32 Mini Kit, two mini-DIN plugs, and the published parts; its joystick numbers are swapped relative to the C64 firmware.

The official C64, A500, and 800XL Tindie pages were out of stock on 2026-07-30, although the project marks those models active and supported. CBMretro had equivalent cased C64/C128 and A500/A1200 hardware available at EUR 41.90; the original designer does not support third-party builds. Open hardware, firmware, and documentation remain available. The guide's original Unijoysticle tile is folded here as the retired WiFi predecessor: it needed a separately powered ESP8266 receiver and phone or desktop client, unlike the Bluetooth successor.

Adds Wi-Fi BBS and Hayes-modem access through the user port of supported Commodore computers.

For this system (exact model): The official manual names the Plus/4 and installs the standard WiModem through its user port.

The standard display-free version and both PET versions were out of stock on 2026-07-30. The standard OLED page still said a new design was pending and did not offer ordering. Check the direct pages for a restock or revised design.