Crt Controls Unit A5; Description - Fluke PM3082 Service Manual

UNIT DESCRIPTIONS
5.5

CRT CONTROLS UNIT A5

5.5.1

Description

Each rotary can occupy 4 different states. A rotary incorporates a rotor contact that can make contact
with one of the two stator contacts. It is also possible that the rotor makes no contact. The last
possibility is that the rotor makes contact with both stator contacts. Most of the rotaries are present
on front unit A4. Via connector X5201 the rotaries on the CRT controls unit A5 are read out. The
rotaries are read out via the ROT-BUS lines RA, RB, RC and RD that are made low one at a time.
This results in a certain bit pattern at the input of key latch D5002 on unit A4. This bit pattern is read
by the microprocessor via enable signal PSEN-LT from the front processor on unit A4.
Diodes are used throughout the key and rotary matrix to guarantee that false information is not read
by the microprocessor in case more than one control is operated at a time.
Note: The connectors X5001 on unit A4 and X5201 on unit A5 have opposite numeration.
5.5-1