Measurement Computing USB-4301 - Manual (Page 15)

USB-4301 User's Guide Functional Details
15
Digital input control terminal (DI CTL) for pull-up/down configuration
All digital input pins are floating by default. When inputs are floating, the state of unwired inputs is undefined
—they may read high or low. You can use the DI CTL connection (pin 19) to configure the inputs to read a high
or low value when they aren’t wired.

To pull up the digital pins to +5 V — inputs read high when unwired — wire the DI CTL terminal pin to a
+5V terminal pin (pin 8 or 18).
 To pull down the digital pins to ground — inputs read low when unwired — wire the DI CTL terminal pin
to a GND terminal pin (pin 10, 20, 38, or 48).
The DI CTL connection pulls the inputs to +5V or GND through a 47 k Ω resistor.
Interrupt input terminal (INT)
You can configure the interrupt input terminal (pin 9) with InstaCal to trigger off rising or falling edge inputs.
You can program this pin to perform the following tasks:

Send an event notification to the computer. The transfer rate is system-dependent.
 Latch in the digital inputs. With this option, the current value of the digital inputs (0 or 1) is read and
stored. The stored value is updated when an active edge occurs on this pin.
 Latch out the digital outputs. With this option, digital outputs are not set to the value written until an active
edge occurs on this pin.
 Save the current value of a counter. You can configure this option for each counter individually.
Oscillator output terminal (OSC)
The oscillator output terminal (pin 7) outputs a configurable clock frequency. You can select the source of the
oscillators and also select dividers for the oscillators programmatically to set the output rate.
Ground terminals (GND)
The ground ( GND ) connections (pin 10, 20, 38, or 48) provide a common ground for the digital and voltage
output connections.
Oscillator output (OSC)
You can set the oscillator input programmatically to one of five internal frequency sources or one of 10 external
input pins. The oscillator output can be divided by any number from 1 to 16 before being output to the OSC pin.
Internal sources
The base frequency for the internal frequency sources can be set through InstaCal to one of four different
frequencies — 1.0000 MHz, 1.6667 MHz, 3.3333 MHz, or 5.0000 MHz. This base frequency is used to
generate the five internal frequency sources — FREQ1 through FREQ5.
FREQ1 is the same as the base frequency and each successive internal frequency following FREQ1 divides the
base frequency by another multiple of 10, for example FREQ2 is the base frequency divided by 10, FREQ3 is
the base frequency divided by 100, and so on. This is illustrated in the following table.