M16C62_M Datasheet, PDF (363/615 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/60 SERIES

Timer B
Mitsubishi microcomputers
M16C / 62A Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
2.3.4 Operation of Timer B (pulse period measurement mode)
In pulse period/pulse width measurement mode, choose functions from those listed in Table 2.3.3. Op-
erations of the circled items are described below. Figure 2.3.8 shows the operation timing, and Figure
2.3.9 shows the set-up procedure.
Table 2.3.3. Choosed functions
Item
Set-up
Count source O Internal count source (f1 / f8 / f32 / fc32)
Measurement O Pulse period measurement (interval between measurement pulse falling edge to falling edge)
mode
Pulse period measurement (interval between measurement pulse rising edge to rising edge)
Pulse width measurement (interval between measurement pulse falling edge to rising edge,
and between rising edge to falling edge)
Operation (1) Setting the count start flag to “1” causes the counter to start counting the count source.
(2) If a measurement pulse changes from “H” to “L”, the value of the counter goes to “000016”,
and measurement is started. In this instance, an indeterminate value is transferred to the
reload register. The timer Bi interrupt request does not generate.
(3) If a measurement pulse changes from “H” to “L” again, the value of the counter is transferred
to the reload register, and the timer Bi interrupt request bit goes to “1”. Then the value of the
counter becomes “000016”, and the measurement is started again.
Note
• The timer Bi interrupt request bit goes to “1” when an effective edge of a measurement pulse is
input or timer Bi is overflowed. The factor of interrupt request can be determined by use of the
timer Bi overflow flag within the interrupt routine.
• The value of the counter at the beginning of a count is indeterminate. Therefore, the timer Bi
overflow flag may go to “1” and timer Bi interrupt request may be generated during the interval
between a count start and an effective edge input.
• The timer Bi overflow flag is indeterminate after reset. The timer Bi overflow flag goes to “0” if
timer Bi mode register is written to when the count start flag is “1”. This flag cannot be set to “1”
by software.
Measurement of pulse time interval from falling edge to falling edge
(1) Start count
(2) Start measurement (3) Start measurement again
Count source
“H”
Measurement pulse
“L”
Reload register ← counter
transfer timing
Timing at which counter
reaches “000016”
“1”
Count start flag
“0”
(Note 1)
Transfer
(indeterminate value)
(Note 1)
Transfer
(measured value)
(Note 2)
Cleared to “0” when interrupt request is accepted, or cleared by software
Timer Bi interrupt
“1”
request bit
“0”
Timer Bi overflow flag
“1”
“0”
Note 1: Counter is initialized at completion of measurement.
Note 2: Timer has overflowed.
Figure 2.3.8. Operation timing of pulse period measurement mode
2-46