50
Operation Theory
controls the counter to count up or down (high: count up; low:
count down), while the GPTC_GATE input is a control signal
which acts as a counter enable or a counter trigger signal under
different applications. The GPTC_OUT will then generate a pulse
signal based on which timer/counter mode you have set.
All input/output signals 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.
General Purpose Timer/Counter Modes
Ten 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 reloads the initial value to the counter. The operation
remains halted until the software-start is executed again. The
operating theories under different modes are described in the
following sections.
Mode1: 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 the software application. Current count value can be read-
back by software any time with no effect to the counting.
GPTC_GATE is used to enable/disable counting. When
GPTC_GATE is inactive, the counter halts the current count
value. Figure 4-18 illustrates the operation with initial count = 5,
count-down mode.
Figure 4-18: Mode 1 Operation
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