User`s guide

1-111
Making Measurements
Using Test Sequencing
TTL Input Decision Making Five TTL compatible input lines can be used for decision
making in test sequencing. For example, if a test fixture is connected to the parallel port
and has a micro switch that needs to be activated in order to proceed with a measurement,
you can construct your test sequence so that it checks the TTL state of the input line
corresponding to the switch. Depending on whether the line is high or low, you can jump to
another sequence. To access these decision making functions, press . Refer
to Figure 1-80 for input bus pin locations.
lets you select the single bit (0 − 4) that the sequence will
be looking for.
lets you jump to another sequence if the single input bit you
selected is in a high state.
lets you jump to another sequence if the single input bit you
selected is in a low state.
Pin assignments:
• pin 1 is the data strobe
• pin 16 selects the printer
• pin 17 resets the printer
• pins 18-25 are ground
Electrical specifications for TTL high:
• volts(H) ≥ 2.7 volts (V)
• current = 20 microamps (µA)
Electrical specifications for TTL low:
• volts(L) ≤ 0.4 volts (V)
• current = 0.2 milliamps (mA)
Figure 1-80 Parallel Port Input and Output Bus Pin Locations in GPIO Mode
Seq
TTL I/O
PARALL IN BIT NUMBER
PARALL IN IF BIT H
PARALL IN IF BIT L