Front Unit A4; Signal Name List A4 - Fluke PM3082 Service Manual

UNIT DESCRIPTIONS
5.4

FRONT UNIT A4

5.4.1 Description
Diagram 1
The front unit incorporates several keys and a number of rotary knobs that are read by a
microcomputer D5001. This microcomputer can communicate with the instrument's main
microprocessor on unit A3 via connector X5002. The communication from front unit A4 to unit A3
occurs via buffer D5003. The communication in the opposite direction happens via buffer D5006. The
flipflops D5004 are used to facilitate this communication.
If unit A3 wants to write information to front unit A4 the following occurs:
D5006 is loaded with 8 bits of information via write pulse UFOWR-LT. This pulse is also applied to
flipflop D5004/11 and this makes CPDAV-LT low. This causes an interrupt for the front processor
D5001. D5001 reads D5006 via the signal CPURD-LT.
If the front A4 wants to send information to A3 the following occurs:
D5003 is loaded with 8 bits of information via write pulse CPUWR-LT. This pulse is also applied to
flipflop D5004/3 and this makes UFODAVLT low. This is recognized by the main microprocessor on
unit A3. This device reads the contents of D5003 via signal UFORD-LT.
The rotaries and the keys are read via the 4 bit ROT-BUS and the 8 bit SW-BUS respectively. One
bit in these busses is made low at a time and via the 8 bit UFOAD-BUS an 8 bit pattern is sent back
to processor D5001. This bit pattern incorporates information concerning the keys/rotaries that are
activated.
Diagram 2
The keys and rotaries are both grouped in a matrix. The key position is read out by making one of the
SW lines low at a time. If a key is pressed, a low level is switched through to one of the 8 input lines
of key latch D5002. The other lines stay at a high level via the pull-up resistors R5121 through R5129.
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 X5001 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. This bit pattern is read by the
microprocessor via enable signal PSEN-LT.
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.
5.4.2

Signal name list A4.

Note: In the signal name list you find the itemnumberofthe component that is source or destination.
Behind this itemnumber (separated by
source/destination can be found.
NAME
PSEN-LT
UFODAVLT
UFOWR-LT
MEANING
READ SIGNAL FOR KNOBS AND KEYS
FRONT WRITES TO MICROPROCESSOR
MICROPROCESSOR WRITES TO FRONT
you find the number of the diagram where the
SOURCE DESTINATION
D5001:01
D5004:01
X5002:01
5.4-1
D5002:02
X5002:01
D5006:01
D5004:01