Keithley 708A Instruction Manual Download

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IEEE-488 Programming

5-9

5.7.3 LOCAL/DIGITAL I/O key

This key is used to place the Model 708A in local (while the
Model 708A is in remote) or in digital I/O mode (while in
local). While in the digital I/O mode, an I/O will appear on
the LED matrix (Figure 5-8).

LOCAL

— With the Model 708A in remote, press this key

to return the Model 708A Switching System to local mode
(REM off). It allows operation of all other front panel con-
trols unless the Model 708A is in LLO (Local Lockout).

DIG I/O

— With the Model 708A in local, pressing this key

selects the digital I/O display mode (Figure 5-8). Press this
key a second time to return to local mode from digital I/O
display mode.

IN (input) — Displays the present status of the digital input
on the LED matrix. Logic high is indicated by a lit LED. The
digital input display status is continually updated.

OUT (output) — Displays the present status of the digital
output on the LED matrix. The output can be changed by
clicking the light pen on the appropriate LED. Output high is
indicated by a lit LED. Output low is indicated by an extin-
guished LED. The digital output display status is updated
when the output is changed. Output is negative true when
high LED is on and output is low (sinking).

Table 5-6

Digital input display format

Row/column

Input #

Row/column

Input #

B1
C1

G1
H1

1
2
3
4
5
6
7
8

B2
C2

G2
H2

10
11
12
13
14
15
16

Figure 5-8

Digital I/O status display mode

5.7.4 Concurrent front panel and bus operation

Fundamentally, there is no reason why you cannot control
the instrument simultaneously from the front panel and over
the IEEE-488 bus. However, the following points should be
kept in mind.

1. All front panel keys except for LOCAL are inoperative

while the Model 708A is in remote (REM on). The unit
is placed in remote by addressing it to listen with the
REN line true. Thus, to control the unit from the front
panel, it is necessary to press LOCAL after program-
ming over the bus. Note that LOCAL is also inoperative
if the LLO (Local Lockout) command is in effect.

2. Front panel parameter modification should always be

completed before attempting to use bus control. For
example, you should not attempt to program a setup
over the bus while editing a setup from the front panel.

5.8

General bus command programming

5.8.1 Overview

General bus commands are those commands (such as DCL)
that have the same general meaning regardless of the instru-
ment. Commands supported by the Model 708A are listed in
Table 5-8, which also lists BASIC statements necessary to
send each command. Note that commands requiring that a
primary address be specified assume that the Model 708A
primary address is set to 18 (its factory default address).

5.8.2 REN (remote enable)

The remote enable command is sent to the Model 708A by
the controller to set up the instrument for remote operation.
Generally, the instrument should be placed in the remote
state before you attempt to program it over the bus. Setting
REN true does not actually place the instrument in the
remote state. Instead the instrument must be addressed to lis-
ten after setting REN true before it goes into remote.

Table 5-7

Digital output display format

Row/column

Output #

Row/column

Output #

A11

B11
C11

D11

E11

F11

G11
H11