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Register-Level Programming Chapter 4
Lab-NB User Manual 4-16 © National Instruments Corporation
8253 Counter/Timer Register Groups
The eight registers making up the two Counter/Timer Register Groups access the two onboard
8253 Counter/Timers. Each 8253 has three counters. For convenience, the two Counter/Timer
Groups and their respective 8253 integrated circuits have been designated A and B. The three
counters of group A control onboard DAQ timing and waveform generation. The three counters
of group B are available for general-purpose timing functions.
Each 8253 has three independent 16-bit counters and one 8-bit Mode Register. The Mode
Register is used to set the mode of operation for each of the three counters.
Bit descriptions for the registers in the Counter/Timer Register Groups are given in the following
pages.