Flow Control (Signal Handshaking) - Keithley 6430 Instruction Manual

13-18 Remote Operations

Flow control (signal handshaking)

Signal handshaking between the controller and the instrument lets the two devices commu-
nicate with each other about readiness to receive data. The SourceMeter does not support hard-
ware handshaking (flow control).
Software flow control is in the form of XON and XOFF characters and is enabled when
XON-XOFF is selected from the RS-232 FLOW CONTROL menu. When the input queue of
the unit becomes more than 3/4 full, the instrument issues an XOFF command. The control
program should respond to this and stop sending characters until the SourceMeter issues the
XON, which it will do once its input buffer has dropped below half-full. The SourceMeter rec-
ognizes XON and XOFF sent from the controller. An XOFF will cause the instrument to stop
outputting characters until it sees an XON. Incoming commands are processed after the <CR>
character is received from the controller.
If NONE is the selected flow control, there will be no signal handshaking between the con-
troller and the SourceMeter. Data will be lost if transmitted before the receiving device is ready.
RS-232 connections
The RS-232 serial port is connected to the serial port of a computer using a straight-through
RS-232 cable terminated with DB-9 connectors. Do not use a null modem cable. The serial port
uses the transmit (TXD), receive (RXD), and signal ground (GND) lines of the RS-232 stan-
dard. Figure 13-4 shows the rear panel connector for the RS-232 interface, and Table 13-2
shows the pinout for the connector.
If your computer uses a DB-25 connector for the RS-232 interface, you will need a cable or
adapter with a DB-25 connector on one end and a DB-9 connector on the other, wired straight
through (not null modem).
Figure 13-4
RS-232 interface connector
RS-232
5 4 3 2 1
9 8 7 6
Rear Panel Connector