Microprocessor Pc3 . 1.769.320; Microprocessor System - Revox B225 Maintenance Instructions Manual

WmrMM R^I/OX
• B225 • SECTION 3/3
3.2 Microprocessor PCB 1.769.320
The microprocessor system and the drawer control are
implemented on the microprocessor PCB 1.769=320.
3.2.1 Microprocessor system
The master microprocessor (M-jiP, IC2 ) scans the keyboard
(POO to P G 5 , P10 to P 1 4 ) . The microprocessor system is
reset when the LOAD key is pressed. To enable
differentiation between a power failure and a LOAD
command, P15 of the master processor is also pulled to
"L
fI
in conjunction with a LOAD command. Capacitor C12
latches this condition until P15 is read. This
unconventional circuit arrangement offers the advantage
that a RESET command can be initiated at any time by
pressing the LOAD key in the event that the system
becomes blocked for any reason.
The commands from the IR receiver or the REMOTE socket
are read through the interrupt input of the master
processor . When a command arrives from the IR remote
control, the IR-REC signal is switched to "LOW" for
approximately one second, causing the LED in the IR
receiver window to turn on (command acknowledgment).
The signals B R A ^ T O S
3
! and DRA-POS-F supply the processor
with drawer position information.
The signals CLK, DATA, DLEN-1, and DLEN-2 control the
two LCD drivers PCE 2111 (on PCB 1.769.250).
The gain of the headphones amplifier and the
VARIABLE OUTPUT is controlled by the signals CLK, DATA,
and DLEN-3 (on PCB 1.769.280).
The slave microprocessor (S-]iP, IC4 ) processes the
subcode (supplementary information on the compact disk
such as track, time, e t c . ) . The required signals
originate from PCB 1.769.300 (IC13, SAA 7010, signals
Q-SYNC, SWCLK, Q-DATA, and P - B I T ) .
The-signals RC-0 and RC-0 switch the radial-control
loop on or o f f . When the radial control loop is switched
off (RC-0 = L ) , the laser pick-up can be repositioned
with the signals RCl, RC2, CUR-SUM, and CUR-DIR.
The track signal (TRK) is read through the interrupt
input of the slave processor. This signal changes to
" L " as soon as the laser pick-up passes over a track. The
direction in which the laser pick-up moves is reported
to the slave processor by the signal Tl. This signal
also changes to "L" as soon as the laser pick-up passes
over a track. It is also used in search mode for counting
the tracks. Because the counting speed of the
microprocessor is not high enough, only every other track
is counted in fast search mode (division by 2, I C 6 b ) .
Any program entered through the keyboard Is stored
serially ,in.IC5 (serial R A M ) .
Both microprocessors are initialized by IC1 (reset chip
TL 7 7 0 5 ) . The +5 V STBY supply is supervised by ICl
via pin 7. A reset is also ' initialwai via
R
l /
R
8 , and C8
when the LOAD key is pressed.
Commands from a cable-type remote control can be read
through the REMOTE socket (pin 2 and pin 3 ) . These
commands are electrically isolated through the
optocoupier IC 12a. These signals are converted to
TTL signals by the comparator circuit (IC9a, R 4 4 , R45,
R 4 8 , and R 6 0 ) . In order to disable the commands from
the infrared receiver, the voltage at pin 4 must be
higher than on pin 2 by +5 V. The +5 V STBY of the REMOTE
socket can be used for this purpose (interconnect pins 1
and 2, pins 4 and 5 ) . The IR signal is thus short-
circuited via DLQ2, R41, R42, R43, R 6 2 , and IC9b.