Closing And Opening Channels; Scanning Channels; Reading Input Channels - Keithley 7021 Instruction Manual

Operation

Closing and opening channels

NOTE
This procedure applies to multiplexer
channels (channels 1!1 through 1!30) and
digital output channels (1!31 through
1!40). Digital input channels are read only.
A channel is turned on (closed) by keying in the channel as-
signment and pressing CLOSE. For example, to turn on
(close) channel 36 (Output 36 of Digital I/O) of a card in-
stalled in slot 2, key in the following channel list and press
CLOSE:
SELECT CHANNELS 2!36
The above closed channel can be turned off (opened) by
pressing OPEN or OPEN ALL. The OPEN key turns off
(opens) only the channels specified in the channel list, and
OPEN ALL turns off (opens) all channels.
NOTE
For the Model 7002 mainframe, you can
use the light pen to turn output channels on
and off.
The following display is an example of a channel list that
consists of several channels:
SELECT CHANNELS 2!1, 2!3, 2!22-2!25
Notice that channel entries are separated by commas (,). A
comma is inserted by pressing ENTER or the right cursor
key ( ). The channel range is specified by using the hyphen
(-) key to separate the range limits. Pressing CLOSE will
close all the channels specified in the channel list. Pressing
OPEN (or OPEN ALL) will open the channels.
Channel patterns can also be used in a channel list. This al-
lows you to control specific bit patterns for logic circuits.
Example:
SELECT CHANNELS 2!1, M1
Pressing CLOSE will turn on channel 2!1 and the channels
that make up channel pattern M1. Refer to the mainframe
instruction manual for information on defining channel
patterns.
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Scanning channels

Channels are scanned by creating a scan list and configuring
the Model 7001/7002 to perform a scan. The scan list is cre-
ated in the same manner as a channel list (See the Closing
and opening channels paragraph). However, the scan list is
specified from the SCAN CHANNELS display mode. (The
SCAN LIST key toggles between the channel list and the
scan list.) The following shows an example of a scan list:
SCAN CHANNELS 2!1, 2!3, 2!21-2!25
When a scan is performed, the channels specified in the scan
list will be scanned in the order that they are presented in
the scan list.
Channel patterns can also be used in a scan list. This allows
you to control specific bit channels or bit patterns. For
example:
SCAN CHANNELS M1, M2, M3, M4
When M1 is scanned, the channels that make up channel
pattern M1 will turn on. When M2 is scanned, the M1 chan-
nels will turn off and the channels that make up M2 will turn
on. M3 and M4 are scanned in a similar manner. Refer to
the instruction manual for the mainframe for information on
defining channel patterns.
A manual scan can be performed by using the RESET de-
fault conditions of the Model 7001/7002. RESET is selected
from the SAVESETUP menu of the main MENU. When
RESET is performed, the mainframe is configured for an in-
finite number of manual scans. The first press of STEP takes
the mainframe out of the idle state. The next press of STEP
will close the first channel specified in the scan list. Each
subsequent press of STEP will select the next channel in the
scan list.

Reading input channels

Input channels are read from the READ-I/O-CARD option
of the CARD CONFIG MENU of the mainframe. This
menu is accessed by pressing the CARD key. In this "read in-
put channels" display mode, the mainframe displays the real-
time state of each input channel.
Input channels use positive true logic but can be configured
to pull up or pull down. Open inputs will read high (on) if in-
puts are configured for pull up. Conversely, open inputs will
read low (off) when configured for pull down. To configure
pull-up resistance, refer to Section 4.