Appendix 1: Pulse Signal Detection - NorthStar Z80 Manual

APPENDIX I". PULSE SIGNAL DETECTION
Some steps in the checkout procedure will"require test equipment
capable of distinguishing a signal containing pulses from a DC
signal. Anyone of the following will suffice.
1. Use of an oscilloscope is best since the shape and frequency
of the pulses can also be determined.
2. Use a logic probe that detects pulses.
3~
If the ZPB is being assembled for use with a HORIZON, then use
a counter on the motherboard to divide the frequencies down to
the audio range and then play the result through a hi-fi
amplifier. To do this, remove the 74LS16l at location 7D on
the motherboard. Then attach the test probe wire to jumper 2D
pin 16 (this is the input to the divider). Next, take the
output of the divider at jumper l0A pin 11 and connect to the
AUX input of the audio amplifier. Finally, connect the AUX
input ground on the audio amplifier to signal ground on the
motherboard. This arrangement will divide high frequency
signals by 4096 and thus put the resulting signal in the
audible range. Thus a 4 MHz signal will be heard as a tone
one octave higher than a 2MHz signal.
4. Construct the "probe" shown in figure lC on a piece of
cardboard or perf-board. This probe converts high frequency
signals to DC signals. The voltage of the resulting DC signal
will be pr6portional to the duty factor of the tested wave
form.
North Star Z80A PROCESSOR BOARD
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