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Model 3750
Keithley Instruments, Inc. Multifunction I/O Card
28775 Aurora Road
Cleveland, Ohio 44139
1-888-KEITHLEY
40 Digital I/O, 2 Analog Outputs, 4 Counters
www.keithley.com


GENERAL
Channels 1 - 5: Bidirectional, high current digital I/O (40 bits)
Channels 6 - 9: 32-bit counter (4 counters)
Channels 10 - 11: Isolated voltage and current analog outputs (2 each)




DIGITAL I/O1
Configuration: 40 bidirectional digital I/O bits arranged in 5 banks of 8 bits each. Each bank can be configured for either
input or output capability. 1 bank of I/O is equivalent to 1 system channel.

Digital Input specifications:
An internal weak pull-up resistor of approximately 68 k is provided on the card for each I/O. This pull-up resistor can be
removed via onboard jumper on a channel (8 bit) basis. The pull-up voltage can either connect to the internally supplied
5V or an externally supplied voltage of up to 30V via onboard jumper. An internal 5V supply connection is separately
available to run external logic circuits.

Digital Input logic low voltage: 0.8V max
Digital Input logic high voltage: 2V min.
Digital Input logic low current: -600uA max @ 0V
Digital Input logic high current: 50uA max @ 5V

Logic: Positive True.
2
System Input Minimum Read speed : 1000 readings / second.
Maximum externally supplied pull-up voltage: 30V
Maximum externally supplied voltage to any digital I/O line: Pull-up voltage (5V internal or up to 30V external)

1
All channels power up configured as inputs.
2
All channels configured as inputs.
Specifications are subject to change without notice.
SPEC-3750 Rev. A / July 2008 Page 1 of 4
Model 3750
Keithley Instruments, Inc. Multifunction I/O Card
28775 Aurora Road
Cleveland, Ohio 44139
1-888-KEITHLEY
40 Digital I/O, 2 Analog Outputs, 4 Counters
www.keithley.com

Digital Output specifications:
Each output has an internal fly-back diode for driving inductive loads. Each output is protected against continuous short
circuits and over temperature. An internal 5V supply connection is separately available to run external logic circuits.

Digital Output logic high voltage: 2.4V minimum @ Iout = 10mA. sourcing only.
Digital Output logic low voltage: 0.5V maximum @ Iout = -300mA sinking only.

Maximum output sink current: 300mA per output, 3.0 A total per card.

Logic: Positive True.
3
System Output Minimum Write speed : 1000 readings / second.
Maximum externally supplied voltage to any digital I/O line: Pull-up voltage (5V internal or up to 30V external)

Alarm: Trigger generation is supported for a maskable pattern match or state change on any of channels 1 through 5.
Protection: Optional disconnect (set to inputs) during output fault conditions.
Internal 5V logic supply: The internal logic supply is designed for powering external logic circuits of up to 50mA
maximum. The logic supply is internally protected with a self-resetting fuse. Fuse reset time < 1 hour.




3
All channels configured as outputs.
Specifications are subject to change without notice.
Page 2 of 4 SPEC-3750 Rev. A / July 2008
Model 3750
Keithley Instruments, Inc. Multifunction I/O Card
28775 Aurora Road
Cleveland, Ohio 44139
1-888-KEITHLEY
40 Digital I/O, 2 Analog Outputs, 4 Counters
www.keithley.com


COUNTER / TOTALIZER INPUT
Maximum Count: 2 32 - 1
Maximum Input Rate: 1 MHz, rising or falling edge, programmable.
Minimum Input pulse width: 500 ns
Input Signal Level: 200 mVp-p (minimum), 42V Peak (maximum)
Threshold: AC (0V) or TTL Logic Level
Gate Input: TTL-HI (Gate+), TTL-LO (Gate-) or NONE.
Minimum Gate input setup time: 1us
Count Reset: Manual or Read + Reset
System Input Minimum Read speed: 1000 readings / second.
Alarm: Trigger generation is supported for a count match or counter overflow on any of channels 6 though 9

ANALOG VOLTAGE OUTPUT
The isolated analog voltage output is designed for general purpose, low power applications.
4
Output Amplitude