Owners manual

2: Configuring Modbus
Modbus Protocol User Guide 12
Serial Protocol (1=Modbus/RTU, 2=Modbus/ASCII)
Serial Modbus comes in two forms. Modbus/RTU uses 8-bit data bytes to send binary
information. However, some devices cannot handle 8-bit data bytes, so
Modbus/ASCII is used. Modbus/ASCII is a slower protocol, where each 8-bit data
byte is converted to 2 ASCII characters. Since the IAP Device Server converts both
to and from Modbus/TCP fully, you can mix any combination of RTU and ASCII
devices on a Modbus/TCP network. So a Modbus/RTU master attached to one IAP
Device Server can remotely access a Modbus/ASCII slave attached to another IAP
Device Server.
Interface Type (1=RS232 2=RS422/RS485+4-wire 3=RS485+2-wire)
This allows the IAP Device Server to deal with the software-related details of using
RS232, RS422, and RS485.
With the XPress DR-IAP, you still must set the external red RS232/RS485 switch
appropriately. With the UDS-10-IAP or CoBox-FL-IAP, you must still select the
correct pins for RS232 or the shared RS422/485 pins.
Enter Serial Parameters (B,D,P,S)
Enter the baud rate (300/ 600/ 1200/ 2400/ 4800/ 9600/ 19,200 or 38,400), data bits
(7/8), parity (N/O/E), and stop bits (1/2) in the classic “DOS Mode Command” style.
Examples are 9600,8,E,1 or 1200,7,O,2. These settings must match the settings on
the attached Modbus device.
These settings are valid with the XPress DR-IAP only. The UDS-10-IAP and CoBox-
FL IAP also support baud rates 57,600 and 115,200. The UDS-10-IAP supports only
1 stop bit. If you try to set an unsupported combination of settings, a warning
displays.
Note: Regardless of these settings, IAP Device Server configuration is
always done on CH1 with RS232 and a setting of 9600,8,N, 1.
Modem Control Settings
When using RS232, the IAP Device Server has a number of user-definable “Modem
Control” parameters to manage RTS/CTS handshaking for half-duplex radio
modems.
RTS/CTS Mode (1=Fixed 2=Variable)
Answer 1 and the IAP Device Server output is fixed to high. Answer 2 to enable
modem handshaking. The RTS/CTS output is active when the device server is
transmitting on the serial port. This setting is very different from the hardware or
RTS/CTS flow-control used with printers. This mode cannot work with a direct RS232
cable, as each end only asserts its RTS control signal to power up intermediate
transmitters.
The XPress DR-IAP has a DTE-style RS232 port, so RTS is an output and CTS is an
input. The UDS-10-IAP and CoBox-FL-IAP have a DCE-style RS232 port, so RTS is
an input and CTS is an output.