Basic Function Principles

The KL6021 serial interface terminal enables the connection of devices with RS485 interface. Data can be exchanged with the controller in full/half duplex mode, independent of the higher-level bus system. The receive buffer has 128 bytes, the transmit buffer 16 bytes. The data transfer between terminal and controller is handled via a handshake in the status and control byte. The factory setting of the terminal is 9600 baud, 8 data bits, 1 stop bit, no parity, full duplex mode.

LED display

The Run LED indicates the operating state of the terminal.

Alternative output format for process data

In the alternative output format, 4 or 5 bytes are mapped in the Bus Coupler (3 bytes for data and 1 or 2 control/status byte(s)). The KL6021 is delivered in the alternative format. The mapping of the terminal in the alternative format is described in more detail in the chapter Terminal configuration.

Standard output format for process data

In the standard output format, 4 bytes are mapped in the Bus Coupler (3 bytes for user data and 1 control/status byte). By changing the parameters of the KL6021, up to 5 bytes of user data can be transferred.


The chapter on "Access from the user program" contains an overview of possible mapping configurations, depending on the configurable parameters.

Connection for RS485 transfer

In RS485 mode, data is transmitted in half duplex mode. A bus structure can be created in this operation mode.

Basic Function Principles 1:
Connection for RS485 transfer

Connection for RS422 transfer

In RS422 mode, data is transmitted in full duplex mode. Only peer-to-peer connections can be established.

Basic Function Principles 2:
Connection for RS422 transfer