Digital Outputs - Keithley 2750 User Manual

9-6 Limits and Digital I/O

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
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
Control
Line
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
Model 2750
33V
Digital Output
Flyback Diode
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.
Model 2750 Multimeter/Switch System User's Manual
Pin 7 (+5V to +33V)
+5V
4.75kΩ
(Pull-up)
Digital Output
Pin 9 - Digital Ground
Figure 9-3.