Editing Acorn 6502 Second Processor (section)

=== Links ===

The links are hard-wired for normal use.<ref name="sm" /> Section 5.4 of the hosted manual misnumbers the first of them; the circuit diagram shows it as LK1.<ref name="cct" />

* LK1 powers the whole unit from the BBC Micro's supply. The second processor's own supply leads must be disconnected first, and Acorn advises against it because it may overload the BBC Micro's supply.
* LK2 connects HIRQ, the interrupt from the second processor to the host. Standard software does not use it, and with LK2 made the BBC Micro will not work while the second processor is switched off.
* LK3 selects where the host half of the Tube ULA gets its power. Acorn says it must not be altered.
* LK4 stands in for diode D1, which is not fitted because the disable feature was not implemented.
* LK5 sets the refresh rate for a 4 MHz processor and must not be changed at 3 MHz.<ref name="sm" />