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Introduction
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5
Serial communications
5.1
Introduction
•
2-wire EIA RS485 via a RJ45 connector
•
Modbus RTU protocol supported (see Chapter 6 CT Modbus RTU on page 16 for details).
A serial communications link enables one or more drives to be used in a system controlled by a host controller such as a PLC (Programmable Logic
Controller) or computer. The communications link uses the EIA, also known as RS485, as standard for the hardware interface. The EIA422 (RS422)
hardware interface is also supported.
The Commander SK has a standard 2-wire EIA485 half-duplex interface that enables all drive set-up, operation and monitoring to be accomplished if
required. Therefore it is possible to control the drive entirely through the EIA485 interface without the need for other control cabling etc.
A host controller can operate up to 32 EIA485 devices with the use of one line buffer. Further line buffers will increase this number, if necessary.
Each transmitter/receiver within the Commander SK loads the EIA485 lines by 2 unit loads (with any termination and pull-up and pull-down resistors
disconnected). This means that up to 16 drives can be connected in a single group to one line buffer. When additional line buffers are used, up to
247 drives can be operated by a host controller.
5.2
EIA232 to EIA485 communications
An external EIA232 hardware interface such as a PC can be used with a suitable converter. This converter must have the hardware and software
support to tri-state the transmit buffer following the message transmission. Otherwise, the Commander SK EIA485 transmitter will not be successful
in transmitting a reply as the host transmitter will cause contention on the 2-wire interface.
Examples of EIA232 to EIA485 converters (one to one)
•
CT Comms cable (CT part number 4500-0087)
•
USB Comms cable (CT part number 4500-0096)
•
Amplicon 485Fi
CT Comms cable is specifically designed to convert EIA232 to EIA485 with Control Techniques products.
NOTE
These converters are for one to one connection between a PC and the Commander SK drive, they do not have multi-drop capability.
NOTE
The CT Comms cable is an isolated converter. It has reinforced insulation as defined in IEC60950 for altitudes up to 3,000 metres and has been
designed to connect the Commander SK to equipment such as lap-top computers.
5.2.1
CT Comms cable
CT Comms cable enables the use of serial communications with the Commander SK drive using a software package such as CTSoft. This allows
access to all of the drives parameters and advanced function menus.
CT Comms cable is only intended for the purpose of commissioning a drive. Therefore:
•
It is not suitable for permanent installation
•
It does not provide connectivity to an EIA485 based network
When this converter is used with a Commander SK and a true EIA232 host/master such as a PC, then no external power supply is required. This is
because the converter sources its power from both the drive and the EIA232 port. However, if the converter is attached to a host/master device that
does not have a standard EIA232 port, then an external power supply may be required.
CT Comms cable does not directly use any of the hand shaking functions that are available on a standard EIA232 port, but does utilise 2 of the hand
shaking pins (pins 4 and 7) as a source of power. If these signals are not available, then a +10V supply should be applied to pins 4 and 7 with respect
to pin 5 of the 9-way D-type connector.
Table 5-1 CT Comms cable 9 way D-Type pin functions
EIA232 9-way
D-type connector
1
2
3
4
5
6
7
8
9
12
Parameter
Keypad and
display
communications
Pin function
Not connected
TX
RX
DTR
GND
Not connected
RTS
Not connected
Not connected
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Commander SK Advanced User Guide
Issue Number: 9
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