Chapter 7
Digital I/O
©
National Instruments Corporation
7-3
DAQ-STC Technical Reference Manual
7.4.1.1 Parallel Input
In parallel input mode, an external device transfers 8-bit parallel data to the DAQ-STC
through the DIO lines. Typically, software configures the external device to place a new data
byte on the DIO lines based on EXTSTROBE/SDCLK, which is under software control. The
DAQ-STC then reads the data lines after each EXTSTROBE/SDCLK pulse. Figure 7-2 shows
a parallel input operation where the external device sends a new data byte on each
EXTSTROBE/SDCLK falling edge. The DAQ-STC reads the data bytes 0x55 and 0xAA hex.
Figure 7-2.
Parallel Input
7.4.1.2 Parallel Output
In parallel output mode, the DAQ-STC transfers 8-bit parallel data to an external device
through the DIO lines. Typically, the software configures the external device to read a new
data byte based on EXTSTROBE/SDCLK, which is under software control. The software
then updates the DIO lines between each EXTSTROBE/SDCLK pulse. In this mode, the
software must be careful not to exceed the maximum data transfer rate of the receiving device,
or data loss may result. Figure 7-3 shows a parallel output operation where the external device
receives a new data byte on each EXTSTROBE/SDCLK falling edge. The DAQ-STC
transmits the data bytes 0x55 and 0xAA hex.
Figure 7-3.
Parallel Output
SW READ
SW READ
EXTSTROBE/SDCLK
DIO<7..0>
0xAA
0x55
SW UPDATE
SW UPDATE
EXTSTROBE/SDCLK
DIO<7..0>
0xAA
0x55