Functional Description

20.6.6 Gated Time Accumulation Mode

Setting the PAMOD bit configures the PA for gated time accumulation operation. An active level on the PAI pin enables a divide-by-64 clock to drive the PA. The PA edge bit, PEDGE, selects low levels or high levels to enable the divide-by-64 clock.

The trailing edge of the active level at the PAI pin sets the PA input flag, PAIF. The PA input interrupt enable bit, PAI, enables the PAIF flag to generate interrupt requests.

NOTE

The PAI input and GPT channel 3 use the same pin. To use the PAI input, disconnect it from the output logic by clearing the channel 3 output mode and output level bits, OM3 and OL3. Also clear the channel 3 output compare mask bit, OC3M3.

The PA counter register, GPTPACNT, reflects the number of pulses from the divide-by-64 clock since the last reset.

NOTE

The GPT prescaler generates the divide-by-64 clock. If the timer is not active, there is no divide-by-64 clock.

PULSE

ACCUMULATOR

CHANNEL 3 OUTPUT COMPARE

OM3

OL3

OC3M3

PAD

Figure 20-22. Channel 3 Output Compare/Pulse Accumulator Logic

20.6.7 General-Purpose I/O Ports

An I/O pin used by the timer defaults to general-purpose I/O unless an internal function which uses that pin is enabled.

The PORTTn pins can be configured for either an input capture function or an output compare function. The IOSn bits in the GPT IC/OC select register configure the PORTTn pins as either input capture or output compare pins.

The PORTTn data direction register controls the data direction of an input capture pin. External pin conditions trigger input captures on input capture pins configured as inputs.

MOTOROLA

Chapter 20. General Purpose Timer Modules (GPTA and GPTB)

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Motorola MCF5281, MCF5282 user manual Gated Time Accumulation Mode, General-Purpose I/O Ports, Pulse Accumulator, OM3 OL3