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Chapter 4
Signal Connections
DAQCard-DIO-24 User Manual
4-4
©
National Instruments Corporation
Table 4-2 summarizes the port C signal assignments for modes 0, 1,
and 2. Mode 2 is only available for port A. You can configure port A
and port B for two different modes. Any port C lines not configured as
handshaking control lines are available for general-purpose input or
output.
Power-up Pin State Considerations and Defaults
At startup, the ports on the DAQCard-DIO-24 default to mode 0 input,
and all digital lines are pulled up to logic high. In addition, any digital
line that is allowed to float will also be pulled up to logic high. To keep
a digital line at logic low, instead of logic high, at startup or when it is
being allowed to float, connect a 4.7 k
Ω
resistor from the digital line to
ground in parallel with the external device. For example, if you have the
DAQCard-DIO-24 connected to a CB-50 I/O connector block and want
to pull down PC7 to logic low, you can connect a 4.7 k
Ω
resistor from
pin 1 to any even-numbered ground pin on the 50-pin connector.
Table 4-2.
Port C Signal Assignments
Programming
Mode
Port C Data Lines, Upper Nibble
Port C Data Lines, Lower Nibble
PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
Mode 0
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
Mode 1 Input
I/O
I/O
IBF
A
STB
A
*
INTR
A
STB
B
*
IBFB
B
INTR
B
Mode 1 Output
OBF
A
*
ACK
A
*
I/O
I/O
INTR
A
ACK
B
*
OBF
B
*
INTR
B
Mode 2
OBF
A
*
ACK
A
*
IBF
A
STB
A
*
INTR
A
I/O
I/O
I/O
* Indicates that the signal is active low.
Subscripts A and B denote port A or port B handshaking signals.