Acorn BBC Master 128, Руководство по обслуживанию

Страница: 14 / 87

Master Series Service Manual
LK6(0) and LK6(1) plug, made A B: Main Clock Select.
Multi-function link.
This group of 4 pins can take either one or two shorting plugs as
follows:
Link between A and B - The computer main 16MHz reference is provided
by on-board circuitry. This is normally how computers are shipped.
Link between B and D - The computer main 16 MHz reference must be
provided from pin A17 on either of the cartridge connectors. Note that
in this case a clock source MUST be provided or the dynamic memories
could be destroyed.
Link between C and D - The cartridges are clocked by the 8 MHz signal
from the computer. This is a synchronous signal with the 2 MHz (phi2)
signal, also supplied to the cartridges. Note that the link between A
and B must also be fitted.
LK7 PCB track, made East: Video
polarity. Two position link.
The polarity of the video RGB signals is determined by this link. It
is supplied as a track on the bottom of the PCB causing true polarity.
This track must be broken and a piece of wire used to make the link
West for negative polarity.
LK8 : Not present.
LK9 : Not present.
LK10 fitted for NTSC only: Channel Select.
Two position link.
When used with NTSC VHF televisions, the modulator enables one of two
channels to be selected. Note that the computer as supplied for use in
the UK is fitted with a UHF modulator so LK10 is not fitted.
LK11 : Not present.
LK12 Plug, made B (East): CSYNC/Cartridge Machine
Detect. Two position link.
Position A - This connection to the computer CSYNC line is provided
for GENLOCK purposes.
Position B - Certain hardware cartridges may need to detect whether
they are plugged into a Master Series computer or an Acorn Electron.
Master computers are shipped with this link in the B position, causing
a logic LOW to appear on pin A10 of the cartidges. The Electron has no
connection to this pin.
9 Issue 1