IBM 7220, Instruction Manual

Page: 86 / 155

6-10
Chapter 6, COMPUTER OPERATION
6.4 Command Descriptions
This section lists the commands in logical groups, so that, for example, all commands
associated with setting controls affecting the signal channel are shown together.
Appendix E gives the same list of commands but in alphabetical order.
6.4.01 Signal Channel
IMODE [n] Controls whether the instrument input is connected to a current or a voltage
preamplifier
The value of n sets the input mode according to the following table:
n Input mode
0 Current mode off - voltage mode input enabled
1 High bandwidth (HB) current mode enabled - connect signal to B input
connector
2 Low noise (LN) current mode enabled - connect signal to B input connector
If n = 0 then the input configuration is determined by the VMODE command.
If n > 0 then current mode is enabled irrespective of the VMODE setting.
VMODE [n] Voltage input configuration
The value of n sets up the input configuration according to the following table:
n Input configuration
0 Both inputs grounded (test mode)
1 A input only
3 A-B differential mode
Note that the IMODE command takes precedence over the VMODE command.
FET [n] Voltage mode input device control
The value of n selects the input device according to the following table:
n Selection
0 Bipolar device, 10 k
Ω
input impedance, 2 nV/
√
Hz voltage noise
1 FET, 10 M
Ω
input impedance, 5 nV/
√
Hz voltage noise
FLOAT [n] Input connector shield float / ground control
The value of n sets the input shield switch according to the following table:
n Selection
0 Ground
1 Float (connected to ground via a 1 k
Ω
resistor)