Intel 8XC196MD, 8XC196MH, 8XC196MC manual Operating in Compare Mode, Preventing EPA Overruns

EVENT PROCESSOR ARRAY (EPA)

11.4.1.2Preventing EPA Overruns

Any one of the following methods can be used to prevent or recover from an EPA overrun situa- tion.

•Clear EPAx_CON.0

When the overwrite bit (EPAx_CON.0) is zero, the EPA does not consider the captured edge until the EPAx_TIME register is read and the data in the capture buffer is transferred to EPAx_TIME. This prevents overruns by ignoring new input capture events when both the capture buffer and EPAx_TIME contain valid capture times.

•Check for pending EPAx interrupts before exiting an EPAx ISR

Another method for avoiding this situation is to check for pending EPA interrupts before exiting the EPA interrupt service routine. This is an easy way to detect overruns and addi- tional interrupts. It can also save loop time by eliminating the latency necessary to service the pending interrupt. However, this method cannot be used with the peripheral transaction server (PTS).

11.4.2 Operating in Compare Mode

When the selected timer value matches the event-time value, the action specified in the control register occurs (i.e., the pin is set, cleared, or toggled, an A/D conversion is initiated, or the wave- form generator is reloaded). If the re-enable bit (EPAx_CON.3) is set, the action reoccurs on ev- ery timer match. If the re-enable bit is cleared, the action does not reoccur until a new value is written to the event-time register. See “Programming the Capture/Compare Channels” on page 11-18 and “Programming the Compare-only Channels” on page 11-22 for configuration informa- tion.

In compare mode, you can use the EPA to produce a pulse-width modulated (PWM) output. The following sections describe two possible methods.

11.4.2.1Generating a Low-speed PWM Output

You can generate a low-speed, pulse-width modulated output with a single EPA channel and a standard interrupt service routine. Configure the EPA channel as follows: compare mode, toggle output, and the compare function re-enabled. Select standard interrupt service, enable the EPA interrupt, and globally enable interrupts with the EI instruction. When the assigned timer/counter value matches the value in the event-time register, the EPA toggles the output pin and generates an interrupt. The interrupt service routine loads a new value into EPAx_TIME.

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