Glossary
© National Instruments Corporation G-5 653X User Manual
G
group A collection of one, two, or four ports and an associated timing controller. 
All buffered operations must be performed on groups. 
H
handshaking I/O Data-transfer mode in which the 653X device engages in a two-way 
communication with the peripheral device. The 653X asserts a signal, ACK, 
when it is ready for a data transfer and the peripheral device asserts a 
separate signal, REQ, when it is ready for a data transfer. Data is transferred 
only when both the 653X and the peripheral device are ready.
I
interrupt a computer signal indicating that the CPU should suspend its current task 
to service a designated activity
I/O Input/Output—a transfer of data to/from a computer system involving 
communications channels, operator interface devices, and/or data 
acquisition and control interfaces
K
kKilo—the standard metric prefix for 1,000, or 103, used with units of 
measure such as volts, hertz, and meters
L
line Individual digital bit
LSB Least significant bit
low/high Refers to the active, or “on” state of handshaking I/O lines. For example, if 
ACK is active low, the 653X device is ready when its ACK line asserts 
(changes to) low.