8
Chapter 3
Functional Details
Components
The USB-DIO24H/37 has the following external components, as shown in Figure 5.
37-pin I/O connector
USB connector
LED
Figure 4. USB-DIO24H/37 components
37-pin I/O connector
The 37-pin connector provides 24 digital I/O, one counter, six ground, and two power connections.
The digital I/O port is configured as two 8-bit and two 4-bit ports based on an 82C55 mode 0 emulation. You
can configure each port independently for input (default) or output.
The CTR signal is the input to the 32-bit external event counter. The internal counter increments when the TTL
levels transition from low to high. The counter can count frequencies of up to 1 MHz.
The six ground (
GND
) pins are identical and provide a common ground for all USB-DIO24H/37 functions.
The two power pins (
+5V
) draw power from the USB connector. Each pin is a +5 volt output that is supplied by
the computer.