This guide covers everything you need to physically connect a PAX A920 terminal to a PC for serial communication.
The full connection path from PC to terminal:
PC (USB port)
|
v
Prolific PL2303 USB-to-Serial Adapter
|
v
DB9 Female Connector (your custom cable)
|
v (custom 3-wire cable)
|
RJ45 Connector (your custom cable)
|
v
L920-BE Base Station (RS232 port)
|
v (pogo pins / Bluetooth / WiFi)
|
PAX A920 Terminal
The L920-BE base station has an RJ45 port for serial communication, but it is NOT standard Ethernet. You need a custom cable that connects specific RJ45 pins to specific DB9 pins.
Only 3 wires are needed. The other 5 wires in the Cat5e cable are not used.
| RJ45 Pin | Wire Color (T568B) | DB9 Pin | Signal | Function |
|---|---|---|---|---|
| Pin 5 | White/Blue | Pin 3 | TXD | Data transmission |
| Pin 6 | Green | Pin 4 | DTR | Handshake signal |
| Pin 7 | White/Brown | Pin 1 | DCD | Carrier detect |
All other pins on both connectors are left unconnected.
Step 1: Cut the cable
Take a Cat5e or Cat6 network cable and cut it to your desired length (1-2 meters is typical). Strip about 3-4 cm of the outer jacket on both ends to expose the 8 colored wires inside.
Step 2: Identify the three wires
Using the T568B color standard, identify:
You can cut the other 5 wires short since they are not used. However, on the RJ45 end, all 8 wires must still be inserted into the RJ45 plug for a proper crimp.
Step 3: Crimp the RJ45 end
On one end of the cable, crimp a standard T568B RJ45 plug. All 8 wires go into the plug in the standard T568B order (the same way you would make a normal network cable):
Pin 1: White/Orange
Pin 2: Orange
Pin 3: White/Green
Pin 4: Blue
Pin 5: White/Blue <-- ACTIVE
Pin 6: Green <-- ACTIVE
Pin 7: White/Brown <-- ACTIVE
Pin 8: Brown
Clip facing away from you, pin 1 is on the left.
Step 4: Solder the DB9 end
On the other end of the cable, solder only the three active wires to a DB9 female connector:
Leave all other DB9 pins empty. Do not connect ground or any other signal.
Step 5: Test continuity
Using a multimeter in continuity mode, verify:
The L920-BE base broadcasts a WiFi SSID for the A920 terminal to connect to. The PAX A920 will NOT detect or connect to open (no password) WiFi networks. You must set a WiFi password on the base station.
The A920 connects to the base via Bluetooth or the base’s WiFi – this is separate from the RS232 serial connection to your PC.
Configure your COM port with these exact settings:
| Setting | Value |
|---|---|
| Baud Rate | 9600 |
| Data Bits | 8 |
| Parity | None |
| Stop Bits | 1 |
| Flow Control | None |
To set this on Windows: Device Manager > Ports (COM & LPT) > [your COM port] > Properties > Port Settings.
The Prolific PL2303 USB-to-Serial adapter requires a driver. On Windows 10/11, the driver usually installs automatically when you plug in the adapter. If it does not, download the driver from the Prolific website.
After installation, the adapter should appear in Device Manager under Ports (COM & LPT) as something like “Prolific USB-to-Serial Comm Port (COM3)”.
If you are connecting the A920 directly via USB (for ADB debugging or app deployment, not for ECR communication), you need the PAX USB driver. This is separate from the serial adapter driver and is not needed for ECR serial communication.
A detailed SVG wiring diagram is included in this repository at docs/diagrams/PAX_L920BE_Wiring_Diagram.svg. It shows both connectors, all pin positions, the three active wires with their colors, and step-by-step build instructions.