Keithley 2001 Operator's Manual page 152

Front Panel Operation
Digital I/O Receptacle
Pin Designations
1 = Digital Input
2 = N/C
3 = N/C
4 = V ext flyback connection (+5V to +30V)
5 = Digital Ground
6 = Digital Output #1
7 = Digital Output #2
8 = Digital Output #4
9 = Digital Output #3
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Digital I/O port
The Model 2001's Digital I/O port can be used to control
external circuitry. The port provides four output lines and
one input line. Each open-collector output can be set high
(+5V) or low (0V) and will sink up to 100mA. A TTL high
on the Model 2001's digital input is read as "ON". The four
output lines can also operate external supplies from +5V to
+30V.
Use the DIGITAL I/O menu to select the following options:
• OUTPUT-STATE
ON or OFF selectable for each output line (1 through 4).
Use to check or change the output state.
• OUTPUT-SENSE
ACTIVE-HIGH or ACTIVE-LOW selectable for each
output line (TTL1 through TTL4). Use to check or
change the output sense.
• INPUT
ON or OFF. Use to check or change the status of the
digital input line. Sense is fixed at active-high
(ON=5V).
Controlling digital circuitry
Each of the four digital, open-collector outputs (connector
J1031, pins 6 through 9) includes a built-in pull up resistor to
+5V. The output transistor is capable of sinking up to 100mA
from voltages up to +30V. The outputs can be controlled
3-120
5 1
9 6
(Connector J1031)
independently or tied to one of four limit values (two high,
two low). See paragraph 3.12.5
controlling digital outputs from the limits menu.
Early versions of the Model 2001 have an additional 10k
resistor connected between the collector and the internal
built-in test circuitry. Under certain combinations of output
states, this resistor limits the output high to 2.5V. For
example:
Output #1 set high (+5V)
Outputs #2, #3, and #4 set low (0V)
Output #1 is restricted to +2.5V
If using the digital output to sink current from external
devices (see external voltage supply later in this paragraph),
a Model 2001 containing the additional 10k resistor will
function correctly. The transistor switch is open, restricting
current flow through the external device in the high state
(+5V). However, if the output is directly used as an input to
a typical logic input, the 2.5V high state may not be reliably
detected as a high. To correct this condition (if a 2.5V high
is unacceptable), add external 1k pull-up resistors to the
logic circuit inputs, remove the built-in test resistors (R734,
R737, R739, and R741), or use an external voltage supply.
External voltage supply
Each output can be operated from external voltage supplies
(voltage range from +5V to +30V applied through the device
being driven). Refer to
schematic of the digital I/O port. The high current sink
capacity of the output driver allows direct control of relays,
solenoids, and lamps (no additional circuitry needed). Each
output channel contains a fly-back diode for protection when
switching inductive loads (such as a low power solenoid or
relay coils). To use these fly-back diodes, connect the
external supply voltage to pin 4 of J1031 (the digital I/O
port). Make sure the external supply voltage is between +5V
and +30V and current required by the device does not exceed
100mA.
mum current or exceed +30V maximum
voltage on pin 4 of J1031 (the digital I/O
port). Applying current or voltage ex-
ceeding these limits may damage the in-
strument.
2001-900-01 Rev. K/ August 2010
for information on
Figure 3-46 for a simplified