Hardware guide

What cable does my vintage computer need?

Almost every setup is the same chain: your computer's serial port, the right cable, and a USB serial adapter on the Windows PC. Find your machine below for the exact parts, speeds and terminal software.

Vintage computer's serial port→ Null-modem cable / adapter→ USB serial adapter → Windows PC

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The parts almost everyone needs.

Modern PCs don't have serial ports, so a USB serial adapter is the one thing every serial setup needs. Most vintage machines also need a null-modem cable, because both ends are "computers" (DTE).

Our pick

Every serial setup

USB to RS-232 serial adapter

Plugs into the Windows PC and gives you a COM port for RetroModem Bridge. This is the adapter we recommend.

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Most machines

DB-9 null-modem cable

Crosses the send/receive lines so two computers can talk. Female-to-female fits most USB adapters and PC-style ports.

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Saves a trip

DB-9 / DB-25 adapter & gender changer kit

Older machines often use 25-pin ports. A small kit of DB-25 to DB-9 adapters and gender changers covers almost every combination.

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Tandy Color Computer

CoCo 1, CoCo 2, CoCo 3, Dragon

Built-in port: 4-pin DIN "Serial I/O" (the bit-banger), or a cartridge RS-232 Pak / Deluxe RS-232 Pak with a DB-25 connector.
Speed: Keep the bit-banger at 300–2400 baud. An RS-232 Pak (6551 ACIA) handles 9600–19200 on a CoCo 3.
Terminal software: NetMate, Ultimaterm, Greg-E-Term (CoCo 3, 80 columns)
Tested setup: CoCo 3 + Deluxe RS-232 Pak + NetMate at 19200. It's a built-in profile in RetroModem Bridge.

What to buy

With an RS-232 Pak (recommended)

DB-25 to DB-9 null-modem cableFrom the Pak's DB-25 port to the USB adapter
Amazon
USB serial adapterOur pick for the PC side
Amazon

Using the built-in bit-banger port

CoCo 4-pin DIN to DB-9 serial cableOften sold by retro vendors as well
Amazon
USB serial adapterOur pick for the PC side
Amazon

Have a CoCo FujiNet? Skip the cables: turn on RetroModem Bridge's Network Listener and connect over Wi-Fi with N:TELNET://your-pc:2323/.

TRS-80 & Model 100

Model 100/102/200, Model I/III/4 with RS-232 board

Built-in port: Model 100/102/200: DB-25 RS-232 port on the back. Model I/III/4: DB-25 on the optional RS-232 board.
Speed: Up to 19200. On the Model 100, set the speed with TELCOM's STAT (for example 98N1E for 9600 baud).
Terminal software: TELCOM (built into the Model 100/102/200); Omniterm or ST80 on the Model I/III/4

What to buy

DB-25 to DB-9 null-modem cableModel 100 port is female, so get a cable with a DB-25 male end
Amazon
USB serial adapterOur pick for the PC side
Amazon
Gender changer kitHandy if your cable's ends don't match
Amazon

Commodore 64 & 128

C64, C64C, SX-64, C128, VIC-20

Built-in port: The user port. It's 5-volt TTL, not RS-232, so it needs a level-shifting interface.
Speed: 2400 baud with the standard KERNAL routines, 9600 with an UP9600-compatible interface, up to 38400 with a SwiftLink/Turbo232 cartridge.
Terminal software: CCGMS, StrikeTerm, Novaterm

What to buy

User-port RS-232 interfaceMAX232-based, with a DB-9 connector (UP9600 support is a plus)
Amazon
DB-9 null-modem cableFrom the interface to the USB adapter
Amazon
USB serial adapterOur pick for the PC side
Amazon

Never connect a PC-style RS-232 cable straight to the user port. RS-232 voltages can damage the C64.

Apple II

II, II+, IIe, IIc, IIc+, IIgs

Built-in port: II/II+/IIe: a Super Serial Card (or compatible) with a DB-25 cable. IIc: 5-pin DIN serial ports. IIc+ and IIgs: 8-pin mini-DIN serial ports.
Speed: Up to 19200 on the Super Serial Card, IIc and IIgs
Terminal software: ProTERM, Spectrum, ModemWorks, Kermit
Tip: On a Super Serial Card, set the jumper block to MODEM and use a null-modem cable, or set it to TERMINAL and use a straight cable.

What to buy

II / II+ / IIe with a Super Serial Card

DB-25 to DB-9 null-modem cableFrom the card's DB-25 connector
Amazon
USB serial adapterOur pick for the PC side
Amazon

IIc+ / IIgs (and IIc)

Mini-DIN-8 to DB-9 serial cableThe same cable as a classic Mac serial cable. The IIc needs a 5-pin DIN cable instead.
Amazon
DB-9 null-modem adapterAdd this if the cable is straight-through
Amazon
USB serial adapterOur pick for the PC side
Amazon

Atari 8-bit

400, 800, XL, XE

Built-in port: No RS-232. Use the SIO port with an Atari 850 Interface (or a modern equivalent), or a FujiNet.
Speed: Up to 9600 through an 850-style interface
Terminal software: BobTerm, Ice-T

What to buy

With an 850 Interface

DB-9 null-modem cableFrom the 850's serial port to the USB adapter
Amazon
Gender changer kitThe 850's ports are male DE-9
Amazon
USB serial adapterOur pick for the PC side
Amazon

FujiNet owners: no cables needed. Point your Atari terminal at N:TELNET://your-pc:2323/ with RetroModem Bridge's Network Listener turned on.

Atari ST

520ST, 1040ST, STE, Mega ST, TT, Falcon

Built-in port: DB-25 male "Modem" port on the back
Speed: Up to 19200
Terminal software: Flash II, Connect, Freeze Dried Terminal

What to buy

DB-25 female to DB-9 female null-modem cablePlugs straight into the ST's male port
Amazon
USB serial adapterOur pick for the PC side
Amazon

Commodore Amiga

A500, A600, A1200, A2000, A3000, A4000

Built-in port: DB-25 male serial port
Speed: 19200 is easy; faster speeds work on most models
Terminal software: Term, NComm, JR-Comm

What to buy

DB-25 female to DB-9 female null-modem cableFits the Amiga's male serial port
Amazon
USB serial adapterOur pick for the PC side
Amazon

The Amiga 1000 has a female serial port wired differently from later models. Use a cable made for the A1000.

IBM PC & DOS compatibles

PC, XT, AT, 286/386/486 and vintage laptops

Built-in port: COM1/COM2 as a DB-9 male or DB-25 male connector
Speed: Up to 19200 on a 16550 UART (most 386 and later machines); 9600 is safer on an original 8250 UART
Terminal software: Telix, Procomm Plus, Qmodem, Telemate

What to buy

DB-9 female-to-female null-modem cableThe classic "LapLink" style cable
Amazon
USB serial adapterOur pick for the PC side
Amazon
DB-25 to DB-9 adapterOnly if your COM port is 25-pin
Amazon

Classic Macintosh

Mac Plus, SE, Classic, II series, PowerBook (68k)

Built-in port: 8-pin mini-DIN "Modem" port. The Mac 128K/512K use a DE-9 port instead.
Speed: Up to 19200
Terminal software: ZTerm, MicroPhone

What to buy

Mini-DIN-8 to DB-9 serial cablePlug it into the Modem port
Amazon
DB-9 null-modem adapterAdd this if the cable is straight-through
Amazon
USB serial adapterOur pick for the PC side
Amazon

CP/M, TI-99/4A, MSX & more

Kaypro, Osborne, TI-99/4A, MSX and other serial machines

Built-in port: Kaypro and Osborne: DB-25 serial. TI-99/4A: DB-25 on the RS-232 card or sidecar. MSX: an RS-232C cartridge.
Rule of thumb: If it has a 9- or 25-pin serial port and can run a terminal program, it works with RetroModem Bridge.
Terminal software: MEX or Kermit (CP/M), TE II or Fast-Term (TI-99/4A)

What to buy

DB-25 to DB-9 null-modem cableCovers most 25-pin machines
Amazon
Gender changer kitSo the cable fits either way
Amazon
USB serial adapterOur pick for the PC side
Amazon

Troubleshooting

Cable connected but nothing happens?

Four checks fix almost every first-time serial problem.

Null modem or straight?

Two computers need a null-modem cable (send and receive crossed). If you type AT and get nothing back, add or remove a null-modem adapter.

Match the baud rate

The speed in your terminal program and in RetroModem Bridge must be the same. Start at 2400 or 9600, then go faster once it works.

Find the right COM port

Open Device Manager → Ports (COM & LPT) to see your adapter's COM number, then press the rescan button in RetroModem Bridge.

Turn on echo or try DTR/RTS

If you can't see what you type, turn on ECHO. If nothing happens at all, toggle DTR and RTS. Some machines wait for those signals.

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READY.

Got your cable? Get the bridge.

RetroModem Bridge is free. Download it, plug in your adapter and type ATDT MENU.

Download RetroModem Bridge v3.6 Get the USB serial adapter