Programming instructions

Chapter 17 Shaking Hands with a Digital Partner
© National Instruments Corporation 17-3 LabVIEW Data Acquisition Basics Manual
Sending Out Multiple Digital Values
You can group multiple ports together so you can send more digital values
out at a time. The order of grouped ports affects which handshaking lines
you use. If you want to group ports 0 and 1 and you list the ports in the order
of
0:1
, then you should use the handshaking lines associated with port 1.
In other words, always use the handshaking lines associated with the last
port in the list. So, if the ports are listed
1:0
, then you should use the
handshaking lines associated with port 0.
For 8255-based devices that perform handshaking, you must connect all the
STB lines together if you are using more than one port or grouping ports
for digital input, as shown in Figure 17-1. Connect only the IBF line of the
last port in the port list to the other device. No connection is needed for the
IBF signals for the other ports in the port list.
Figure 17-1.
Connecting Signal Lines for Digital Input
Port x
1
STB*
IBF
External Device
(last port in portList)
Port x
n
STB*
IBF
Port
x
2
STB*
IBF