The DYMO/CoStar LabelWriter range of direct thermal label printers includes an RS-232 serial interface using a proprietary Mod 8×8 (8P8C modular) connector on the printer side rather than a conventional D-sub. The cable mates this modular plug to a standard DB9S (9-pin D-sub female) connector on the host computer side, carrying six signals. Default communication settings are 9600 baud, 8 data bits, 1 stop bit, and no parity. RS-232 output levels are −5 V (MARK) and +12 V (SPACE), consistent with TIA/EIA-232-F.
6 pin RJ12 (6P6C) male connector to the LabelWriter
9 pin D-SUB female connector to the computer
| LabelWriter Name | LabelWriter Pin | Direction | computer Pin | computer Name | Description |
|---|---|---|---|---|---|
| CTS | 1 | → | 8 | CTS | Clear to send |
| TXD | 2 | ← | 3 | TXD | Transmit (to LabelWriter) |
| RXD | 3 | → | 2 | RXD | Receive (from LabelWriter) |
| GND | 4 | — | 5 | GND | Ground |
| RTS | 5 | ← | 7 | RTS | Request to send |
| DSR | 6 | → | 6 | DSR | Data set ready |
Notes
- The printer-side connector is a Mod 8×8 (8P8C) modular plug — physically similar to an RJ12/RJ45 housing — not a D-sub; only six of the eight positions are wired.
- The host-side connector is a DB9S (9-pin D-sub female), matching the DTE DE-9 pinout standardised by EIA-574.
- RS-232 output signal levels: MARK (logic 1) = −5 V; SPACE (logic 0) = +12 V.
- Default serial parameters: 9600 baud, 8 data bits, 1 stop bit, no parity.
- CTS (pin 5 of DB9) is software-dependent for flow control; RTS (pin 8 of DB9) signals that the printer is ready to receive data.
Signals
- CTS — Clear to Send; flow-control input to the printer, software-dependent.
- TXD — Transmit Data; serial data sent from the host to the printer.
- RXD — Receive Data; serial data sent from the printer to the host.
- GND — Signal, earth, and power ground reference.
- RTS — Request to Send; output from the printer indicating it is ready to receive.
- DSR — Data Set Ready; output from the printer indicating online status.