Intel 80C196NU, 8XC196NP, Microcontroller manual EPA Simplified Input-capture Structure

8XC196NP, 80C196NU USER’S MANUAL

EPA

Interrupt

Pending Bit

Set

TIMERx

Event Occurs

at EPA Pin

Capture Buffer

EPAx_TIME

Read-out Time Value

A2458-02

Figure 10-6. EPA Simplified Input-capture Structure

If a third event occurs before the CPU reads the event-time register, the overwrite bit (EPAx_CON.0) determines how the EPA will handle the event. If the bit is clear, the EPA ignores the third event. If the bit is set, the third event time overwrites the second event time in the capture buffer. Both situations set the overrun interrupt pending bit, and if the interrupt is enabled, they generate an overrun interrupt. Table 10-4 summarizes the possible actions when a valid event oc- curs.

NOTE

In order for an event to be captured, the signal must be stable for at least two state times both before and after the transition occurs (Figure 10-7).

Event 1

2 State

Times

Event 2

2 State

Times

2State Times

2State Times

A3130-01

Figure 10-7. Valid EPA Input Events

10-10