Agilent Technologies 34972A User Manual page 316

Chapter 7 Tutorial
Multifunction Module
Using an External Pull-Up
In general, an external pull-up is required only when you want to set the
output "high" value greater than TTL levels. For example, to use a +12V
external power supply, the value of the external pull-up resistor is
calculated as follows:
V = 12 VDC
cc
I = I x safety factor = 1 mA x 0.5 + 0.5 ma
max out low
V
12
cc
R = ---------- - = ----------------- -
·
I
0.0005
max
The value of the logic "high" level with the external 24 k pull-up
resistor is calculated as follows:
R
external
V = V x ------------------------------------------------------ -
high cc
R
external
Driving External Switches
You can use two digital output channels to control an external switch.
For example, you can drive the Agilent 876X series of microwave
switches using an external power supply and two digital output
channels. The state of the 2-to-1 multiplexer is changed by setting the
appropriate output bit low (0).
Digital Output Channel
316
= 24 k
= 12 x
--------------------------------------- -
+ R 24 k
external
Agilent 876X Microwave Switch
24 Volt
Power
Supply
24 k
= 8.47 VDC
+ 10 k