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13-18 Remote Operations Models 2500 and 2502 User’s Manual

Terminator

The Model 2500 can be conﬁgured to terminate each program message that it transmits to

the controller with any of the following combinations of <CR> and <LF>:

<CR> Carriage return

<CR+LF> Carriage return and line feed

<LF> Line feed

<LF+CR> Line feed and carriage return

Flow control (signal handshaking)

Signal handshaking between the controller and the instrument lets the two devices com-

municate with each other about readiness to receive data. The Model 2500 does not sup-

port hardware 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 Model 2500

issues the XON, which it will do once its input buffer has dropped below half-full. The

Model 2500 recognizes 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

controller and the Model 2500. Data will be lost if transmitted before the receiving device

is ready.

RS-232 connections

The RS-232 serial port (Figure 13-3) 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 standard. 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

9876

54321

Rear Panel Connector

RS-232

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Keithley 2500 User Manual

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