ADLINK PXI-2006 - Manual (Page 63)

Operation Theory 53
GPTC_GATE, and GPTC_OUT are assumed to be active high or
rising-edge triggered in the figures.
General Purpose Timer/Counter modes
Eight programmable timer/counter modes are provided. All modes
start operating following a software-start signal that is set by the
software. The GPTC software reset initializes the status of the
counter and re-loads the initial value to the counter. The operation
remains halted until the soft-ware-start is re-executed. The operat-
ing theories under different modes are described as below.
Mode 1: Simple Gated-Event Counting
In this mode, the counter counts the number of pulses on the
GPTC_CLK after the software-start. Initial count can be loaded
from software. Current count value can be read-back by soft-
ware any time without affecting the counting. GPTC_GATE is
used to enable/disable counting. When GPTC_GATE is inac-
tive, the counter halts the current count value. Figure 4-23 illus-
trates the operation with initial count = 5, count-down mode.
Figure 4-23: Mode 1 Operation
Mode 2: Single Period Measurement
In this mode, the counter counts the period of the signal on
GPTC_GATE in terms of GPTC_CLK. Initial count can be
loaded from software. After the software-start, the counter
counts the number of active edges on GPTC_CLK between
two active edges of GPTC_GATE. After the com-pletion of the
period interval on GPTC_GATE, GPTC_OUT outputs high and
then current count value can be read-back by software. Figure