ABB RS485 Installation And Startup Manual page 22

Power
Receive
RTS
RTU
RVT
Rx
Signed Integer
Time-out
Transmit
Tri-State
Tx
Unsigned Integer
Word
Xon/Xoff
8.2 References
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8.3 Adequate choice of an RS232-RS485 converter at the computer side
In a RS-485 network, a control of the direction is needed to alternate between
transmission and reception. Two cases may be found:
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22 - Appendix  RS485
IT
Power Factor Controller RVT
Microprocessor based controller from the ABB industrial
controller range. The Power
is intended to switch capacitor in order to compensate the
power factor of the electrical network.
Incoming communication signal. (Rx)
RequestToSend hardware handshaking signal. Used with
ClearToSend.
Remote Terminal Unit
see Power
See Receive
Whole number value represented by 16 bits (-32768 to
32767)
Parameter specifying the max. wait time in ms. waiting for a
response in the range 0..10000 ms.
Outgoing communication signal. (Tx)
The ability of a communications transmitter to turn its
circuitry off, reducing the load on the network
see Transmit
Positive whole number value represented by 16 bits (0 to
65535)
A group of 16 bits
Software implementation of data flow control
Modbus Data Table (RVT Modbus Data Table for the RVT)
RVT Installation and Operating Instructions
Modicon Modbus Protocol Reference Guide (PI–MBUS–300 Rev. J)
No flow control:
The direction control is done in the RS-232 to RS-485 converter. The converter
senses the data direction and release automatically the line to tristate when no
activity is found. The release time is typically one character length (11 bits /
baudrate).
RTS flow control:
The direction control is done by setting RTS signal (Request To Send) and
releasing RTS after transmission. This is done by software. The drawback
that if the software is busy by another task or if the PC is too slow, the direction
control may be inverted too late, loosing received data.
In Modbus RTU framing, messages start with a silent interval of at least 3.5
character times. The table below is related to the RS-485 Modbus Adapter.
IT
Power Factor Controller RVT
IT
Power Factor Controller RVT
is