UPD75238GJ NEC [NEC], UPD75238GJ Datasheet - Page 75

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UPD75238GJ

Manufacturer Part Number
UPD75238GJ
Description
4 BIT SINGLE-CHIP MICROCOMPUTER
Manufacturer
NEC [NEC]
Datasheet
(4) Configuration and operation when the timer/pulse generator is used in the PWM pulse generation mode
(5) Static output to the PPO pin
Fig. 4-34 shows the configuration when the timer/pulse generator is used in the PWM pulse generation
mode.
The PWM pulse generation mode is selected by setting TPGM0 to 0. TPGM5 and TPGM7 are set to 1 to
enable pulse output. In the PWM mode, the PWM pulse signal can be output on the PPO pin, and IRQTPG
can be set at intervals of a fixed time period (2
PWM pulses output by the PD75238 are active-low and have an accuracy of 14 bits. This pulse signal
is applicable for electronic tuning and control of a DC motor when it is integrated by an external low-pass
filter and is converted to analog voltage. (See Fig. 4-35.)
The PWM pulse signal is generated by combining the basic period determined by 2
at 6.0 MHz)
constant of the external low-pass filter can be decreased.
The low-level width of a PWM pulse depends on the 14-bit modulo latch value. The upper 8 bits of the
modulo latch are sent from the 8 bits of MODH, and the lower 6 bits of the latch are sent from the upper
6 bits of MODL.
When the PWM pulse signal is converted to analog form, the voltage level of the analog output is obtained
as follows:
V
V
To prevent an incorrect PWM pulse from being output by unstable modulo latch data being rewritten, the
instructions, then in the 14-bit data which is to be transferred to the modulo latch at one time. This transfer
operation is referred to as reloading, and it is controlled by TPGM3.
Cautions 1. If the modulo register H (MODH) is set to 0, the PWM pulse generator cannot function
Notes 1. 7.81 ms at 4.19 MHz
When pulse output is unnecessary, the PPO pin can be used as normal static output. In this case, the output
data is set in TPGM4 with TPGM5 being set to 0 and TPGM7 to 1.
PD75238 allows correct data to be written in MODH and MODL beforehand with 8-bit manipulation
AN
ref
: Reference voltage of external switching circuitry
= V
2. 244 s at 4.19 MHz
ref
2. If the lower 2 bits of the modulo register L (MODL) are read, the read result is unpredictable.
3. If the modulo latch is changed in a shorter period than the PWM pulse basic period
Value of modulo latch
Note 2
normally. So be sure to set MODH to a value from 1 to 255.
2
10
/f
X
(171 s at 6.0 MHz)
and the secondary period by 2
2
14
Note 2
, PWM pulses do not change.
15
/f
X
= 5.46 ms at 6.0 MHz)
15
/f
X
(5.46 ms at 6.0 MHz)
Note 1
.
Note 1
so that the time
PD75238
10
/f
X
(171 s
75

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