9-6 Limits and Digital I/O Model 2750 Multimeter/Switch System User’s Manual
Digital outputs
The digital I/O port has five digital outputs. Each digital output can be used as a sink to
control devices (e.g., relays), or as a source to provide input to external logic (TTL or
CMOS) circuitry. The simplified schematic for the digital outputs are shown in Figure 9-3.
Note that this illustration shows the schematic for one digital output. All five digital output
circuits are identical.
Figure 9-3
Digital I/O port simplified schematic
The five digital output lines (pins 1 through 5) are controlled by limit operations. Each of
these five outputs correspond to the following limit operations:
Digital Output 1 — Low Limit 1 (LO1)
Digital Output 2 — High Limit 1 (HI1)
Digital Output 3 — Low Limit (LO2)
Digital Output 4 — High Limit 2 (HI2)
Digital Output 5 — Master Limit (logical OR of the four above limits)
When a limit (LO1, HI2, LO2, or HL2) is reached, the digital output line for that limit will
be pulled high or low. When a reading is within the limit, the output line is released. Digi-
tal output 5 is the logical OR of the four limits. Therefore, if any of the four limits are
reached or exceeded, output 5 will be pulled high or low.
NOTE When the reading is taken and a limit has been reached, there is a short delay
before the digital output line is active. As measured from the output trigger
(TLINK), the delay is about 10msec when closing a channel, and about 2msec
without a channel closure. Because of additional time needed for data cnver-
sion, the delay may be up to 10 times longer for temperature readings. Allow for
this delay when designing test systems.
+5V
4.75kΩ
(Pull-up)
Pin 9 - Digital Ground
Digital Output
Pin 7 (+5V to +33V)
Digital Output
Flyback Diode
Control
Line
33V
Model 2750
2750-900-01.book Page 6 Wednesday, August 3, 2011 7:56 AM
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