Datasheet

Section 15 Asynchronous Event Counter (AEC)
Rev. 2.00 Jul. 04, 2007 Page 329 of 692
REJ09B0309-0200
15.4.2 8-Bit Counter Operation
When bit CH2 is set to 1 in ECCSR, ECH and ECL operate as independent 8-bit event counters.
φ/2, φ/4, φ/8, or AEVH pin input can be selected as the input clock source for ECH by means of
bits ACKH1 and ACKH0 in ECCR, and φ/2, φ/4, φ/8, or AEVL pin input can be selected as the
input clock source for ECL by means of bits ACKL1 and ACKL0 in ECCR. Input sensing is
selected with bits AHEGS1 and AHEGS0 when AEVH pin input is selected, and with bits
ALEGS1 and ALEGS0 when AEVL pin input is selected.
Note that the input clock is enabled when IRQAEC is high or IECPWM is high. When IRQAEC is
low or IECPWM is low, the input clock is not input to the counter, which therefore does not
operate. Figure 15.3 shows the software procedure when ECH and ECL are used as 8-bit event
counters.
Set CH2 to 1
Set ACKH1, ACKH0, ACKL1, ACKL0,
AHEGS1, AHEGS0, ALEGS1, and ALEGS0
Clear CUEH, CUEL, CRCH, and CRCL to 0
Clear OVH and OVL to 0
Set CUEH, CUEL, CRCH, and CRCL to 1
Start
End
Figure 15.3 Software Procedure when Using ECH and ECL as 8-Bit Event Counters
When the next clock is input after the ECH count value reaches H'FF, ECH overflows, the OVH
flag is set to 1 in ECCSR, the ECH count value returns to H'00, and counting up is restarted.
Similarly, when the next clock is input after the ECL count value reaches H'FF, ECL overflows,
the OVL flag is set to 1 in ECCSR, the ECL count value returns to H'00, and counting up is
restarted. When an overflow occurs, the IRREC bit is set to 1 in IRR2. If the IENEC bit in IENR2
is 1 at this time, an interrupt request is sent to the CPU.