Installation and Configuration
Communications
Release 3.1 25
Once flow control is selected as option, two flow control methods are available. You
can use the rear panel XON switch to select either software-based XON/XOFF flow
protocol or hardware-based CTS/RTS or DTR/DSR flow protocol. Table 2.4 shows
the flow control conditions with regards to the markings on the rear panel subplate.
For a diagram of the rear panel subplate, see Figure 2.2, on page 21.
Table 2.4 Hardware/Software Flow Control Selection
Software
Flow Control
This software protocol uses special characters that synchronize device
communications. The device sends the control code XOFF (ASCII value 13 hex)
when it is not ready to receive data. The device sends the control code XON (ASCII
value 11) when it is ready to resume receiving data.
To choose XON/XOFF protocol, select the XON switch position shown in Table2.4.
Hardware
Flow Control
Hardware flow control protocol requires a dedicated control line on the RS-232
cable. The dedicated control line is needed so that the device can signal the controller
when it is ready to receive data. You can designate either RTS/CTS or DTR/DSR
protocol for the RS-232 interface.
Set the XON switch for hardware control using the information in Table2.4. With
hardware flow control selected, RS-232 Interface PCB jumpers J217 and J218
dictate the type of flow protocol. Table2.5, “Jumper/Pin Settings for RTS/CTS Flow
Control (Default)” and Table 2.6, “Jumper/Pin Settings for DTR/DSR Flow Control
(Default)” identify jumper connections and input and output pin designations for
each protocol. See also “Transmit / Receive Pin Selection” on page 26 for RS-232
connector pinouts.
Note:When resetting the flow control switches during a working session, turn the
power supply OFF and then ON again to ensure that the new settings are put into
effect.
Table 2.5 Jumper/Pin Settings for RTS/CTS Flow Control (Default)
XON Switch Setting Condition
1Hardware Flow Control
(CTS/RTS or DTR/DSR protocol)
0Software Flow Control
(XON/XOFF protocol)
Jumper Connections RS-232 Connector Pin
RTS (Input to RS-232) J218 to 2-4 and 3-5 7
CTS (Output to RS-232) J217 to 1-3 and 4-6 8