Table of Contents
Advertisement
CONTROL CIRCUITRY AND DISPLAY
U700 Extension PCB
The main component in the control circuitry is U700 which is based on
the Z8 microprocessor. In some receivers U700 is a custom-masked
single component, but in some receivers it could be a small extension
board containing a standard microprocessor and a separate ROM. This
extension board contains six capacitors (C1, C2, C3, C4, C5 and C6),
three ICs (U1, U3 and U4) and a 4 MHz crystal X1. The parts list is given
at the end of this manual. Note that the C3, C4, C5, C6, U1, U3 and U4
in this list are quite different from the components with those labels
which are on the main PCB. When the extension board is replaced by
the custom-masked U700, X700, C703 and C704 on the main board are
fitted.
U700 Functionality
U700 runs with a 4 MHz clock generated by crystal X700 to perform
the following:
©
it detects and decodes the codes received via the IR beam from
the handset and those from the top panel buttons;
©
it controls and sends text to the on-screen graphics IC;
eit controls the UHF modulator and the frequency synthesis loop
for the tuner;
©
it controls the routing of the video and audio signals;
®
it controls other switching functions such as the LNB supply
switching;
©
it activates the front panel LEDs.
U701 is an EPROM which is used to store information which is set at
the on-screen menus. The graphics generator IC U600 acts as a port
expander for the control lines TV_PIN_8 and TV_PIN_16. the modulator
chip U200 acts as a port expander for the control line bandwidth.
Control Lines
A block diagram of the serial bus interconnections is shown right.
Some of U700's control functions occur via these lines; others have
specific control lines which are described at the relevant points in the
circuit descriptions. Some lines (e.g. LNB_MON) are inputs to U700 to
inform it of conditions arising in the hardware. The line DEC_PIN_8 is
aninput which informs U700 that pin 8 of the DECODER SCART has
gone high. The line VCR__PIN_8 is described on page 21. The TV_PIN_8
line is always an output from U700 and is also mentioned on
page 23.
Reset
A reset is applied to all the microprocessors within the unit (i.e. U700
and also U300 and U303 in the VideoCrypt circuitry) when the +5 V
supply falls to approximately 4.75 V. D17 generates a precise 5.1 V
reference which is divided by R34 and R35 to give a 4.77 V reference to
pin 5 of U2 which is acting as a comparator. if the 5 V supply at pin 6
drops below 4.77 V, the comparator output will fall to 0 V. This in turn
switches off Q9 which shorts C33 to ground and so the RST reset line is
held low. RST stays low until pin 5 of U2 rises above 4.77 V. If the reset
line (RST) is low Q314 and Q315
also switch off; this removes the +27 V
(switched) supply voltage to the card reader circuitry.
CE_LM7001
CE_GRAPHICS
SERIAL_CLK
Ut00
TUNER FS.
MSS 100 Series Satellite Re
RESET
B/NDWIDTH
TW_PINS
TV_PIN_16
ceiver
ENGLISH
Advertisement
Table of Contents
