M37733MHBXXXFP Datasheet, PDF (24/89 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

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MITSUBISHI MICROCOMPUTERS
M37733MHBXXXFP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
(4) Pulse width modulation mode [11]
Figure 26 shows the bit configuration of the timer Ai mode register
during the pulse width modulation mode. In the pulse width modulation
mode, bits 0, 1, and 2 must be set to “1”.
Bit 5 is used to determine whether to perform as the 16-bit length
pulse width modulator or the 8-bit length pulse width modulator. 16-
bit length pulse width modulator is selected when bit 5 is “0” and 8-bit
length pulse width modulator is selected when bit 5 is “1”. The 16-bit
length pulse width modulator is described first.
The pulse width modulator can be started with a software trigger or
with an input signal from a TAiIN pin (external trigger).
The software trigger mode is selected when bit 4 is “0”. Pulse width
modulator is started and pulse is output from the TAiOUT pin when
the timer Ai start flag is set to “1”.
The external trigger mode is selected when bit 4 is “1”. Pulse width
modulator starts when a trigger signal is input from the TAiIN pin when
the timer Ai start flag is “1”. Whether to trigger at the fall or rise of the
trigger signal is determined by bit 3. The trigger is at the fall of the
trigger signal when bit 3 is “0” and at the rise when it is “1”.
When data is written to timer Ai with the pulse width modulator halted,
it is written to the reload register and the counter.
Then when the timer Ai start flag is set to “1” and a software trigger or
an external trigger is issued to start modulation, the waveform shown
in Figure 27 is output continuously. Once modulation is started,
triggers are not accepted. If the value in the reload register is m, the
duration “H” of pulse is
1
!m
selected clock frequency
and the output pulse period is
1
! (2¹⁶ – 1).
selected clock frequency
An interrupt request signal is generated and the interrupt request bit
of the timer Ai interrupt control register is set at each fall of the output
pulse.
The width of the output pulse is changed by updating timer data. The
update can be performed at any time. The output pulse width is
changed at the rise of the pulse after data is written to the timer.
The contents of the reload register is transferred to the counter just
before the rise of the next output pulse so that the pulse width is
changed from the next output pulse.
Undefined data is read when timer Ai is read.
The 8-bit length pulse width modulator is described next.
The 8-bit length pulse width modulator is selected when bit 5 of the
timer Ai mode register is “1”.
The reload register and the counter are both divided into 8-bit halves.
The low-order 8 bits function as a prescaler and the high-order 8 bits
function as the 8-bit length pulse width modulator. The prescaler
counts the clock selected by bits 6 and 7. A pulse is generated when
the counter reaches 000016 as shown in Figure 28. At the same time,
the contents of the reload register is transferred to the counter, and
count is continued.
76 54 3 21 0
111
Addresses
Timer A0 mode register
Timer A1 mode register
Timer A2 mode register
Timer A3 mode register
Timer A4 mode register
5616
5716
5816
5916
5A16
1 1 : Always “11” in pulse width
modulation mode
1 : Always “1” in pulse width
modulation mode
0 ! : Software trigger
1 0 : Trigger at the falling of TAiIN input
1 1 : Trigger at the rising of TAiIN input
0 : 16 bit pulse width modulator
1 : 8 bit pulse width modulator
Clock source selection bit
0 0 : Select f2
0 1 : Select f16
1 0 : Select f64
1 1 : Select f512
Fig. 26 Timer Ai mode register bit configuration during pulse width
modulation mode
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