Acorn BBC Master 128, Руководство по обслуживанию

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Master Series Service Manual
4 Selection links
LK1 PCB track, made A: 1MHz Bus Audio Input/Output
2 position link.
In the-A position the 1MHz Bus signal is an input to the computer's
audio mixer.
In the B position the 1MHz Bus signal is an output from the computer's
audio circuit (Minimum load 1k ohm).
This link is a permanent track in the A position. The track must be
cut before a wire link is used to make the B position.
LK2 PCB track, made: Cartridge -5V
decoupler. One position link.
In some instances, particular cartridge hardware may need a -5V supply
that is decoupled from the main computer -5V load. To do this R9 needs
to be fitted and LK2 which is a track on the circuit board should be
cut.
LK3 : Not present.
LK4 plug, made: Clock chip IRQ.
One position link.
The 6818 clock/RAM chip has a daily alarm function built in. When the
alarm is triggered, the CPU is interrupted via its IRQ line. Removing
the shunt from LK4 disconnects the CPU IRQ line to the clock line.
This function is not supported by the operating system as this feature
may not be present in future versions of the circuit board.
Consequently the clock chip must be directly operated by the
application software.
LK5 PCB track, made East: CSYNC
polarity. Two position link.
The polarity of the composite synchronisation signal is determined by
this link. It is supplied as a track on the PCB causing negative
synchronisation polarity. This track must be broken and a piece of
wire used to make the other side of the link for positive
synchronisation.
8 Issue 1