Renesas H8/38024 Series, Hardware Manual

Page: 414 / 661

Rev. 6.00, 08/04, page 384 of 628
11.3 Operation
11.3.1 Operation
When using the 10-bit PWM, set the registers in the following sequence.
1. Set PWM1 or PWM2 in PMR9 to 1 for the PWM channel to be used, so that pin P9
0
/PWM1 or
P9
1
/PWM2 is designated as the PWM output pin.
2. Set bits PWCRm1 and PWCRm0 in the PWM control register (PWCRm) to select a
conversion period of 4,096/
φ
(PWCRm1 = 1, PWCRm0 = 1), 2,048/
φ
(PWCRm1 = 1,
PWCRm0 = 0), 1,024/
φ
(PWCRm1 = 0, PWCRm0 = 1), or 512/
φ
(PWCRm1 = 0, PWCRm0 =
0). In the case of the H8/38124 Group, select between pulse-division PWM (PWCRm2 = 0)
and event counter PWM (PWCRm2 = 1) output. Refer to section 9.7, Asynchronous Event
Counter (AEC), for information on the event counter PWM (PWM incorporating AEC) output
format.
3. Set the output waveform data in PWDRUm and PWDRLm. Be sure to write in the correct
sequence, first PWDRLm then PWDRUm for the same channel. When data is written to
PWDRUm, the data will be latched in the PWM waveform generator, updating the PWM
waveform generation in synchronization with internal signals.
One conversion period consists of 4 pulses, as shown in figure 11.2. The total of the high-level
pulse widths during this period (T
H
) corresponds to the data in PWDRUm and PWDRLm.
This relation can be represented as follows.
T
H
= (data value in PWDRUm and 4) • t
φ
/2
where t
φ
is the PWM input clock period: 1/
φ
(PWCRm = H'0), 2/
φ
(PWCRm = H'1), 4/
φ
(PWCRm = H'2), or 8/
φ
(PWCRm = H'3).
Example: Settings in order to obtain a conversion period of 1,024 µs:
When PWCRm1 = 0 and PWCRm0 = 0, the conversion period is 512/
φ
, so
φ
must be
0.5 MHz. In this case, tfn = 256 µs, with 1/2
φ
(resolution) = 1.0 µs.
When PWCRm1 = 0 and PWCRm0 = 1, the conversion period is 1,024/
φ
, so
φ
must be
1 MHz. In this case, tfn = 256 µs, with 1/
φ
(resolution) = 1.0 µs.
When PWCRm1 = 1 and PWCRm0 = 0, the conversion period is 2,048/
φ
, so
φ
must
be 2 MHz. In this case, tfn = 256 µs, with 2/
φ
(resolution) = 1.0 µs.
When PWCRm1 = 1 and PWCRm0 = 1, the conversion period is 4,096/
φ
, so
φ
must be
4 MHz. In this case, t
fn
= 256 µs, with 4/
φ
(resolution) = 1.0 µs
Accordingly, for a conversion period of 1,024 µs, the system clock frequency (
φ
) must
be 0.5 MHz, 1 MHz, 2 MHz, or 4MHz.