Chapter 8 Tutorial

Multifunction Module

Multifunction ModuleDigital Input

The HP 34907A module has two non-isolated 8-bit input/output ports which you can use for reading digital patterns.

∙You can read the live status of the bits on the port or you can configure a scan to include a digital read.

∙You can generate an alarm when a specific bit pattern or bit pattern change is detected on an input channel. The channels do not have to be part of the scan list to generate an alarm.

∙The internal +5V pull-up circuitry allows you to use the digital input to detect contact closures like micro-switches or limit switches.

An open input floats to +5V and is read as a “1”. An input shorted to ground is read as a “0”. An example of a contact closure detection channel is shown below.

 

 

+5 V

 

 

 

10 kΩ

 

 

+

 

I/O Line (1 of 8)

 

 

 

Digital Read

–

+TTL

 

 

Reference

 

 

 

(+2.1 V)

Limit Switch

 

 

 

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