14-Bit Pwm Operation - Renesas Hitachi H8S/2194 Series Hardware Manual

21.3

14-Bit PWM Operation

When using the 14-bit PWM, set the registers in this sequence:
(1) Set bit PMR40 to 1 in port mode register 4 (PMR4) so that pin P40/PWM14 is designated for
PWM output.
(2) Set bit PWCR0 in the PWM control register (PWCR) to select a conversion period of either
32768/φ (PWCR0 = 1) or 16384/φ (PWCR0 = 0).
(3) Set the output waveform data in PWM data registers U and L (PWDRU, PWDRL). Be sure
to write byte data first to PWDRL and then to PWDRU. When the data is written in
PWDRU, the contents of these registers are latched in the PWM waveform generator, and the
PWM waveform generation data is updated in synchronization with internal signals.
One conversion period consists of 64 pulses, as shown in figure 21.2. The total high-level width
during this period (T
expressed as follows:
= (data value in PWDRU and PWDRL + 64) × tφ/2
T
H
where tφ is the period of PWM clock input: 2/φ (bit PWCR0 = 0) or 4/φ (bit PWCR0 = 1).
If the data value in PWDRU and PWDRL is from H'3FC0 to H'3FFF, the PWM output stays
high.
When the data value is H'0000, T
= 64 × tφ/2 = 32 ⋅ tφ
T
H
t H1
) corresponds to the data in PWDRU and PWDRL. This relation can be
H
is calculated as follows:
H
1 conversion period
t f1 t f2
t H2
T H = t H1 + t H2 + t H3 + ... + t H64
t f1 = t f2 = t f3 = ... = t f64
Figure 21.2 Waveform Output by 14-Bit PWM
t f63
t H3 t H63
Rev. 2.0, 11/00, page 429 of 1037
t f64
t H64