Supported Hardware
The maximum effective data transfer rate (Bps) depends on the cycle time (T) of the PLC and the number of bits per transferred data byte (LB = 1 start bit + n data bits + p parity bits + m stop bits).
The maximum effective data transfer rate is limited upwards by the physical baud rate programmed in the bus terminal.
Example 1: When using an EL6001 terminal and a baud rate of 9600 baud, a cycle time of maximum 6 ms is necessary.
Example 2: When using a PC COM port and a baud rate of 115200 baud, a cycle time of maximum 2 ms is necessary.
Serial EtherCAT Terminals
EL60xx in 22-byte mode (EP60xx im 22-byte mode)
The serial EtherCAT Terminal is operated in 22-byte mode, so that 22 data bytes can be transferred to and from the terminal. 3 PLC cycles are still necessary for each exchange.
Bps = (LB * 22/3) / T
The terminal is parameterized via the CoE Online tab in the TwinCAT System Manager (double-click the corresponding object).
Serial PC Interface
The serial physical PC interface (COM1, COM2, etc.) is handled by the TwinCAT system similarly to the serial bus terminal and EtherCAT Terminal and uses larger data transfer buffers than the serial Bus Terminal. The library uses a 64-byte buffer, so that up to 64 data bytes can be transferred simultaneously between the PLC and the interface driver. 3 PLC cycles are again needed for the exchange of a data block with the serial PC interface.
Bps = (LB * 64/3) / T
Virtual serial COM port
The TwinCAT system also supports a virtual serial COM port (COM1, ..., COM255), which is available in Windows. In the TwinCAT/BSD operating system the COM port must register as `ttyU0`...`ttyU255` to be supported.
No configuration of the process image in the TwinCAT System Manager is required. The parameterization takes place directly in the PLC using the function blocks provided.
This communication connection is not real-time capable.
The baud rate can be set between 150 baud and 128000 baud. Typical, frequently used baud rates are 9600 or 115200 baud.
 | One port per target system The product is designed for use with a single virtual COM port per target system. However, in principle it is possible to use of several virtual COM ports on one system, provided function tests are carried out. |
Serial bus terminal
KL6xxx in 3-byte mode
The standard version of the serial Beckhoff Bus Terminal is operated in 3-byte mode. In other words, a bus telegram can transmit or receive 3 data bytes to or from the terminal. Since every data exchange between the PLC and the bus terminal requires 3 PLC cycles, the effective transfer rate is one byte per cycle.
Bps = LB / T
| In the case of bus terminals, the K-bus update time of the bus coupler must be considered when selecting the cycle time (see Task configuration). |
KL6xxx in 5-byte mode
The serial bus terminal can be reprogrammed offline by means of a configuration program (Beckhoff KS2000), so that, in 5-byte mode, 5 data bytes can be transferred to or from the terminal. 3 PLC cycles are still necessary for each exchange. The effective data rate for a given cycle time of the PLC is thus 5/3 greater than in 3-byte mode.
Bps = (LB * 5/3) / T
The bus terminals cannot be re-programmed while the PLC is running, since the 3-byte and 5-byte modes differ in the register mapping and in the TwinCAT System Manager configuration.
| In the case of bus terminals, the K-bus update time of the bus coupler must be considered when selecting the cycle time (see Task configuration). |
KL6xxx in 22-byte mode
The serial bus terminal can be supplied with a 24-byte process image as a special type, so that 22 data bytes can be transferred to and from each terminal. 3 PLC cycles are still necessary for each exchange.
Bps = (LB * 22/3) / T
| In the case of bus terminals, the K-bus update time of the bus coupler must be considered when selecting the cycle time (see Task configuration). |