
75
μ
PD75237
(4)
Configuration and operation for use in the PWM pulse generate mode
The timer/pulse generator for use in the PWM pulse generate mode is shown in Fig. 4-34.
The PWM pulse generate mode is selected by setting TPGM0 to “0”. Pulse output is enabled by setting
TPGM5 and TPGM7 to “1”. In the PWM mode, PWM pulse can be output from the PPO pin and the IRQTPG
can be set at the fixed interval (2
15
/f
X
= 5.46 ms : at 6.0 MHz operation)
*1
.
The PWM pulse generated by the
μ
PD75237 is an active-low, 14-bit accuracy pulse. This pulse is converted
to an analog voltage by integrating it using an external low-pass filter and can be applied for electronic tuning
and DC motor control. (Refer to
Fig. 4-35 Example of D/A Conversion Configuration with
μ
PD75237.
)
The PWM pulse is generated by combining the fundamental period determined by 2
10
/f
X
(171
μ
s: at 6.0 MHz
operation)
*2
and the sub period of 2
15
/f
X
(5.46 ms: at 6.0 MHz operation)
*1
and the time constant of the external
low-pass filter can be shortened.
The low-level width of the PWM pulse is determined by the 14-bit modulo latch value. The modulo latch
value is determined as a result of transfer of MODH 8 bits to the most significant 8 bits of the modulo latch
and MODL most significant 6 bits to the least significant 6 bits of the modulo latch.
The digital-to analog converted output voltage is given as
In the
μ
PD75237, all 14 bits can be transferred simultaneously to the modulo latch after correct data has been
written to MODH and MODL by the 8-bit manipulation instruction. This aims at preventing the PWM from being
generated with an unstable value in the process of modulo latch rewrite. This transfer is called “reload” and
is controlled by TPGM3.
Note
1. Setting “0” to modulo register H (MODH) disables the PWM pulse generator to operate normally. Be
sure to set to MODH a value in the range from 1 to 255.
2. When the least significant 2 bits of modulo register L (MODL) are read, an undefined value is read.
3. The fundamental period of the PWM pulse is 2
10
/f
X
(171
μ
s: at 6.0 MHz operation)*2. If the module latch
is changed with a shorter period, the PWM pulse remains unchanged.
* 1.
7.81 ms at 4.19 MHz operation
244
μ
s at 4.19 MHz operation
2.
(5)
Static output to the PPO pin
If pulse output is not necessary, the PPO pin can be used for normal static output. In this case, set output
data to TPGM4 with TPGM5 and TPGM7 set to “0” and “1”, respectively.
V
AN
= V
ref
×
where V
ref
: External switching circuit reference voltage
Modulo latch value
2
14