The NMI ‘Break’ can only be used with NASBUG T4 and
B-BUG. This should be made on a small piece of veroboard
and mounted somewhere appropriate. To connect
it, a wire should be run from pin 8 of IC42 (under the
board)to the input of the circuit. The CPU should be
lifted from the board and pin 17 carefully bent out
horizontal, the CPU may then be replaced. The output of
the circuit is connected to pin 17 of the CPU, using a
‘Soldercon’ pin. DO NOT SOLDER TO THE CPU.
Fig 1. “Snow Plough”
Fig 2. “NMI Break”
Suppose you want to compare HL with DE, without changing
the contents of either register.