Keithley 6514, Instruction Manual

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12-18 Remote Operation
Flow control (signal handshaking)
Signal handshaking between the controller and the instrument allows the two devices to com-
municate to each other regarding being ready or not ready to receive data. Model 6514 does not
support hardware handshaking (flow control).
Software flow control is in the form of X_ON and X_OFF characters and is enabled when
XonXoFF is selected from the RS232 FLOW menu. When the input queue of Model 6514
becomes more than 3/4 full, the instrument issues an X_OFF command. The control program
should respond to this and stop sending characters until Model 6514 issues the X_ON, which it
will do once its input buffer has dropped below half-full. Model 6514 recognizes X_ON and
X_OFF sent from the controller. An X_OFF will cause Model 6514 to stop outputting characters
until it sees an X_ON. Incoming commands are processed after the <CR> character is received
from the controller.
If NONE is the selected flow control, then there will be no signal handshaking between the
controller and Model 6514. Data will be lost if transmitted before the receiving device is ready.
RS-232 connections
The RS-232 serial port can be connected to the serial port of a controller (i.e., personal com-
puter) 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 standard. It does not use the hardware handshaking lines CTS and
RTS. Figure 12-4 shows the rear panel connector for the RS-232 interface, and Table 12-2 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). Table 12-3 provides pinout identification for the 9-pin (DB-9) or
25-pin (DB-25) serial port connector on the computer (PC).
9 8 7 6
5 4 3 2 1
Rear Panel Connector
RS232
Figure 12-4
RS-232 interface connector