Reset - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
- Control of LED's for operating and standby
display.
- Creation of further switching processes,
e.g. ON/OFF, AV transfer, etc.
- Simulation of a clock synchronised by VPS-
information.
- Timer function for programmable discon-
nect time and recording timer.
- Code converter for IR commands for the
remote control of a video recorder via the
AV voltage switching line and the Dolby
surround unit.
RS 232 for communication with the online
-
as well as the DVB module.
- Digital Link Plus
Euro/AV sockets
In order to fulfil the required tasks the follow-
ing circuit components are combined in one
chip:
- C 16 core with CPU and interrupt controller
- 2 kByte XRAM as working memory
- Interface for the external ROM
- Quarz controlled clock generator
- Interface for the three I2C buses
- Multifunctional timer
- IR decoder
- ON/OFF Flip-Flop
- Reset circuit for internal reset
- Reset circuit for external IC's.
- Ports P2 to P6 with 44 input and output
pins.
Many of these functions are implemented not
by the hardware of the processor, but by the
Loewe-specific software.
Document Q 2500
Control for the
4.1.4

Reset

For correct functioning of the device, various
reset pulses are necessary. The first required
is a reset on pin 73 for the SDA 6000, as soon
as its operating voltage U3.3 is available and
the 6 MHz system cycle has run. This reset is
produced by I 2941. After this reset the SDA
6000 starts to operate and implements and
emits control commands.
The microprocessor also has a reset on pin 8,
produced by I 2946, if the circuit power supply
has run and all IC's have an operating volt-
age. This reset is retarded in SDA 6000 and
then emitted from pin 100 to the digital IC's.
3
RESET digital component input pin 8
The reset for this input is formed by a steep
positive flank. As U3,3 is the last voltage
switched by the power supply unit, this reset is
coupled to the voltage. The reset pulse is cre-
ated in I 2946 and is present on pin 8 of the
microprocessor, if all IC's in the chassis have
an operating voltage. SDA 6000 can then be-
gin controlling the IC's. In addition the proces-
sor also reacts, if the reset is not present on
pin 8 or during operation. Normally 5 V is al-
ways felt on a reset input, provided the device
is fully switched on.
RESET digital component output pin 100
Via this pin the microprocessor sends the re-
set to the other circuits. This is coupled to in-
put pin 8. In this way the processor can moni-
tor the reset, and for transient voltage failures
can prevent, the level on the reset line col-
lapsing. On the other hand, the circuit also
makes it possible for the SDA 6000 to emit a
software controlled reset on pin 50 during op-
eration
In standby and on start up L level is initially
felt on pin 100. Not until the SDA 6000
switches pin 100 to H level, does the L/H flank
produce the reset for the IC's. During opera-
tion the reset inputs must be held permanently
at H level, otherwise the working register will
be deleted.
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