Mini RS232 to RS422/RS485 Serial Adapter / Converter CS-428/9AT-mini2

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The SystemBase CS-428/9AT-mini2 converts RS232 signals to RS422 or RS485 and is the smallest converter available on the market. It is a fast and efficient solution to overcome the distance limitations of RS232 or for connecting to industrial devices with an RS422 or RS485 interface.

No additional software is required for operation. With an easily accessible DIP switch, you can configure the interface for RS422 or RS485. The CS-428/9AT-mini2 is fully compatible with the serial COM port on your PC.


  • Maximum Communication Speed: 921.6Kbps
  • Industrial Grade Temperature: -40~85°C (IEC 60068-2-30/33)
  • RS422/RS485 side: absorb 400W surge from waveform of 10/1000μs peak pulse
  • ESD Protection 15kV (IEC 61000-4-2: ESD level 4 protection)
  • External power not required (When DTR signal line is enabled)
  • Hardware-based Auto Toggling
  • RS422/RS485, Termination Resistor, and Echo mode selectable by external switches
  • Max. 10 Devices Connectable for RS422 Multi-Drop Mode
  • Power: 9~12V, 500mA

Auto RTS Control (Auto Toggling)

The CS-428/9AT-mini2 has a built-in hardware feature that performs automatic toggling to prevent devices from sending data simultaneously. This operation is crucial when multiple devices are connected to prevent electrical collisions that lead to errors and unstable communications.

What is RS485 Echo Mode?

Different from RS485 Non-echo mode, RS485 Echo Mode enables the output signal line to function as the input signal. Therefore, it is not necessary to read the echoed data to confirm whether the data sent crashes with data sent by another device. With the CS-428/9AT-mini2, all operations are controlled by the hardware so no additional modifications are required to the application program.

Using 4-Wire RS485

4-Wire RS485 networking is the same as RS422 Multi-Drop networking. An RS422 device is used as the master and an RS485 device is used as the slave on a 4-Wire RS485 bus. While RS422 and RS485 have different electrical standards, most manufacturers make ICs that use both the RS422 and RS485 interface.

Therefore, RS422 Multi-Drop and 4-Wire RS485 can be considered equal. However, there can be a difference in how software controls them. We engineered our converter to operate with both interfaces regardless of how the application software works.

CS-428/9AT-mini2 Specifications:


  • Maximum Speed: 921.6 Kbps
  • Maximum Distance: 1.2 Km. 24AWG twisted pair cable
  • Connectors:
    • RS232: DE-09S (DB9 Female)
    • RS422/RS485: Terminal Block 5 Pins
  • Signal Lines:
    • RS232: TXD, RXD, RTS, DTR, GND
    • RS422: TXD+, TXD-, RXD+, RXD-
    • RS485: TRXD+, TRXD-
  • RS422 Mode: Point to Point, Multi-Drop
  • RS485 Mode: Echo, Non-Echo
  • DIP Switch: RS422/RS485 selectable


  • Dimensions (W x L x H): 36 x 34.3 x 16.5 mm (1.41 x 1.35 x 0.65 inches)
  • Weight: 20g / 0.71oz

Operating Environment

  • Operating Temperature: -40~+85 C
  • Storing Temperature: -40~+85 C
  • Humidity: 5~95% Non-Condensing


  • Certificates: CE, KC

Package Includes:

1X CS-428/9AT-mini2 Miniature RS232 to RS422/RS485 Serial Adapter / Converter,
Download Guide, Warranty Policy

Additional Resources:

CS-428/9AT-mini2 Manual, Utilities and Specifications Downloads (SystemBase Website)