AV8 Display Board
Refer to circuit diagram L898 sheet 1
Introduction
The AV8 display board contains the front panel graphical
VFD display module, buttons, LEDs, remote IR receiver
and encoder.
The graphical VFD display receives data directly from the
micro on the digital board (via SK100).
Power Supply
The supply rails are supplied to the Display PCB Via
SK100 from the digital board.
Please note that the supply rail marked P36VF1 has been
reset to a voltage of +21volts, this is because the display
was found to be to bright when supplied with +36volts.
LEDs
These are driven using two 74HCT595 (IC101 and IC102)
output latches controlled via SK100 by the micro on the
digital board.
! LED 100 is a bi-colour LED and is used for
standby.
! LED 101 to LED 110 are function and source
indicators.
Remote receiver
The remote receiver (RX101) output is buffered via a
74HC14D (IC104) this is then connected to the digital
board via SK100 pin15 .
Volume/encoder
The encoder (SW124) output A and B is buffered via a
74HC14D (IC104) as PHASE A and PHASE B to the
digital board via SK100 pins 12,13.
Keyboard
The keyboard is polled using a 74HCT595 (IC100), this is
controlled by the micro on the digital board which scans
the keyboard output.
Scanning sequence:
! The outputs of IC100 Q0 to Q7 are set low in
sequence
! The keyboard lines KB0, KB1 and KB2 are
read
When a key is pressed it will result in a low on KB0, KB1
or KB2.
The micro knows which output has been polled low
(IC100 Q0 to Q7) and which line is low KB0, KB1 or KB2
and therefore the intersecting point will represent the key
which has been pressed e.g. Q2 is polled low and KB1 is
read as low mean s that the “CD” button has b een pres sed.