7220 Datasheet, PDF (92/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

FUNCTIONAL DESCRIPTION
2.10 PWM
2.10.2 14-bit PWM (DA output)
The 14-bit PWM automatically outputs a PWM rectangular waveform from the D-A pin by writing high-order
8 bits of the output data to the DA-H register and the low-order 6 bits to the DA-L register. Data of the
DA-H register are transferred to the 14-bit PWM circuit when writing to the DA-L register.
The following explains the output operation of 14-bit PWM rectangular waveform (when f(XIN) = 8 MHz).
ŒThe repeat cycle “T” (4,096 µs) of output waveform is divided into 2⁶ = 64 smaller interval “t” (t =
64 µs). The “t” is further divided into the minimum resolution bit “τ” of 2⁸ = 256 (τ = 0.25 µs).
The HIGH duration of the fundamental waveform is determined by the high-order 8 bits “DH” of the DA
latch.
HIGH duration (time) = τ ! DH (when f(XIN) = 8 MHz, 0.25DH µs)
Because the DH values are “0” to “255,” the HIGH duration can be selected a total of 256.
ŽThe smaller interval “tm” with a longer HIGH level area by “τ” is specified by the low-order 6 bits “DL” of
the DA latch. The tm is specified from among 64 smaller intervals (t0 to t63).
Therefore, a rectangular waveform consisted of 2-kind waveforms with different HIGH duration are output
from pin D–A (a length of entirely HIGH output cannot be output).
Figure 2.10.3 shows the 14-bit PWM output example, Table 2.10.2 shows the relation between DL and tm
(m = “0” to “63”).
Table 2.10.2 The relation between DL and tm (m = “0” to “63”)
Smaller intervals that HIGH duration is longer by τ
Low-order 6-bit data of DA register (DL)
tm (m = “0” to “63”)
MSB _{0 0 0 0 0 0} LSB
Nothing
000001
m = 32
000010
m = 16, 48
000011
000100
000101
000110
:
001000
:
m = 16, 32, 48
m = 8, 24, 40, 56
m = 8, 24, 32, 40, 56
m = 8, 16, 24, 40, 48, 56
:
m = 4, 12, 20, 28, 36, 44, 52, 60
:
010000
:
100000
m = 2, 6, 10, 14, 18, ... 46, 50, 54, 58, 62
:
m = 1, 3, 5, 7, 9 ... 55, 57, 59, 61, 63
:
:
101000
m = 1, 3, 5, 7, 9 ... 52, 55, 57, 59, 60, 61, 63
:
:
111111
m = 1 to 63 (“0” is not included)
Number
0
1
2
3
4
5
6
:
8
:
16
:
32
:
40
:
63
7220 Group User’s Manual
2-65