Serial Interface COM2¶
The serial interfaces COM1 and COM2 are designed according to the standard EIA RS-485. Both interfaces can be operated in RS-485 mode.
| Standard of the serial interfaces | RS-485 |
| Interface connectors | COM1: 9-pole Sub-D connector (female) COM2: 5-pole connector with screw-type connection (optional) |
| Electrical isolation | none |
| Serial interface parameters | Configurable by the software |
| Operating modes | Programming or data exchange |
| Supported protocols | MODBUS or serial data exchange using special software function blocks |
The serial interface COM2 is connected via a 5-pole terminal block and can be used for
- online access
- free protocol communication
- MODBUS RTU, client and server
Note
The serial RS-485 Interface is not electrically isolated.
Note
It is not intended to use COM2 to establish a CS31 system bus.
If the RS-485 bus is used, each interconnected bus line (each bus segment) must be electrically terminated. The following is necessary:
- 2 resistors of 120 Ohm each at both line ends (to avoid signal reflections)
- A pull-up resistor at RxD/TxD-P and a pull-down resistor at RxD/TxD-N. These 2 resistors care for a defined high level on the bus, while there is no data exchange.
Note
The pull-up and the pull-down resistors are included inside the Processor Module’s serial RS-485 adaptor. The termination resistor is not included inside the Processor Module and must be connected externally.
It is useful to activate both the pull-up and the pull-down resistors, which are only necessary once on every bus line, at the bus master. For this reason, these 2 resistors are already integrated within the COM2 interface of the Processor Module. They can be activated by connecting the terminals 1-2 and 3-4 of COM2.
Note
For equipping AC500-eCo Processor Modules with a real-time clock and a second serial RS-485 interface COM2, use TA562-RS-RTC serial RS-485 and real-time clock adaptor TA562-RS-RTC - Adapter with Serial RS-485 (COM2) and Real-time Clock.
| Serial Interface | Pin | Description |
|---|---|---|
| 1 | Terminator P | |
| 2 | TxD/RxD-P | |
| 3 | TxD/RxD-N | |
| 4 | Terminator N | |
| 5 | Functional earth |
The following figure shows an RS-485 bus with the bus master at the line end.
If the master is located within the bus line, it does not need a terminating resistor. The pull-up and the pull-down resistors, however, are necessary:
Attention
:strong:Risk of EMC disturbances!
Unshielded cables may cause EMC disturbances.
Always use shielded cables and connect the shield at every device.
Attention
:strong:Risk of malfunctions!
The pull-up resistors must be used only one time within a bus line.
Use the pull-up resistors only at 1 master.
Note
The ground potential of the interface COM2 is internally connected to the M terminal of the CPU power supply connector.
The cable shields must be earthed. See CS31 System Bus CS31 bus.