ADLINK Technology USB-1901, User Manual

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58 Operation
or down (high: count up; low: count down), while the GPTC_GATE
input is a control signal acting as a counter enable or counter trig-
ger signal in different applications. The GPTC_OUT then gener-
ates a pulse signal based on the timer/counter mode set.
All input/output signal polarities can be programmed by software
application. For brevity, all GPTC_CLK, GPTC_GATE, and
GPTC_OUT in the following illustrations are assumed to be active
high or rising-edge triggered.
4.8 General Purpose Timer/Counter Modes
Ten programmable timer/counter modes are available. All modes
initialize following a software-start signal set by the software. The
GPTC software reset initializes the status of the counter and
reloads the initial value to the counter. The operation remains
halted until software start is executed again. Operations under dif-
ferent modes are described as follows.
4.8.1 Mode 1: Simple Gated-Event Counting
In this mode, the counter calculates the number of pulses on the
GPTC_CLK after a software start. Initial count can be loaded from
the software application. Current count value can be read back by
software any time with no influence on calculation. GPTC_GATE
enables/disables calculation. When GPTC_GATE is inactive, the
counter halts the current count value. Operation in which initial
count = 5, countdown mode is shown.
Figure 4-18: Mode 1-Simple Gated-Event Calculation
5 5 4 3 2 1 1 0 ffff
Gate
CLK
Count value
Software start