Measurement Computing USB-1208FS-Plus - Manual (Page 15)

USB-1208FS-Plus User's Guide Functional Details
15
Digital I/O
The device has 16 DIO channels that are configured as two 8-bit ports – Port A and Port B. Port B is high drive.
You can connect up to eight DIO lines to
Port A0 to Port A7 and up to eight DIO lines to Port B0 to Port B7 .
You can configure each port for either input or output. The digital ports are set for input when the device is
powered on or reset.
When configured for input, the digital I/O terminals can detect the state of any TTL-level. Refer to the
schematic shown in Figure 8.
Figure 8. Schematic showing switch detection by digital channel Port A0
If you set the switch to the +5V input, Port A0 reads TRUE (1). When set to GND, Port A0 reads FALSE (0).
Pull-up/down configuration
All digital I/O lines are pulled high to USB +5 V with a 47 kΩ resistor by default. You can change the
pull-up/down configuration using the internal jumper labeled
DIO . You must remove the device housing to
access the jumper on the circuit board.
Complete the following steps to set the jumper for pull-up or pull-down:
1. Unplug the device from the computer.
2. Turn the device over and rest the top of the housing on a flat, stable surface.
Caution! The discharge of static electricity can damage some electronic components. Before removing the
USB-1208FS-Plus from its housing, ground yourself using a wrist strap or touch the computer
chassis or other grounded object to eliminate any stored static charge.
3. Remove the three screws from the bottom of the device using a #1 Philips head screwdriver.
4. Hold both the top and bottom sections together, turn the device over and rest it on the surface, then
carefully remove the top section of the case to expose the circuit board.
The user-configurable jumpers are labeled DIO A and DIO B . Figure 9 shows the location of each jumper on
the circuit board.
Figure 9. Pull-up/down jumper locations
5. Set each jumper for pull-up (P/UP) or pull-down (P/DN), as shown in Figure 10. Use the jumper labeled
DIO A to configure Port A, and DIO B to configure Port B.