Datasheet

Section 15 Asynchronous Event Counter (AEC)
Rev. 2.00 Jul. 04, 2007 Page 328 of 692
REJ09B0309-0200
15.4 Operation
15.4.1 16-Bit Counter Operation
When bit CH2 is cleared to 0 in ECCSR, ECH and ECL operate as a 16-bit event counter.
Any of four input clock sources—φ/2, φ/4, φ/8, or AEVL pin input—can be selected by means of
bits ACKL1 and ACKL0 in ECCR. When AEVL pin input is selected, input sensing is selected
with bits ALEGS1 and ALEGS0.
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 15.2 shows the software procedure when ECH and ECL are used as a 16-bit event
counter.
Clear CH2 to 0
Set ACKL1, ACKL0, 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 15.2 Software Procedure when Using ECH and ECL as 16-Bit Event Counter
As CH2 is cleared to 0 by a reset, ECH and ECL operate as a 16-bit event counter after a reset,
and as ACKL1 and ACKL0 are cleared to B'00, the operating clock is asynchronous event input
from the AEVL pin (using falling edge sensing).
When the next clock is input after the count value reaches H'FF in both ECH and ECL, ECH and
ECL overflow from H'FFFF to H'0000, the OVH flag is set to 1 in ECCSR, the ECH and ECL
count values each return 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.