National Instruments 700 - Manual (Page 44)

Chapter 4 Theory of Operation
© National Instruments Corporation 4-7 DAQCard-700 User Manual
Digital I/O Circuitry
The DAQCard-700 has 16 digital I/O lines that are TTL-compatible. Pins DIN<0..7> of the I/O
connector are digital input lines, and pins DOUT<0..7> are digital output lines. These lines are
monitored or driven by the Digital Input Register or the Digital Output Register, respectively.
Reading the Digital Input Register returns the current state of DIN<0..7> lines. Writing the
Digital Output Register drives the new value onto DOUT<0..7> lines. The external device may
drive the EXTINT* signal to signal the readiness of data transfer. Figure 4-4 shows a diagram of
this circuitry.
PC I/O Channel
Status
Register
PCMCIA
I/O Channel
Digital
Output
Register
8
/
8
/
Digital
Input
Register
I/O Connector
Interrupt
Interface
EXTINT*
8
/
8
/
I/O RD
I/O WR
DIN <0..7>
DOUT<0..7>
Figure 4-4. Digital I/O Circuitry Block Diagram