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7220 Group User’s Manual

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).

The repeat cycle “T” (4,096 µs) of output waveform is divided into 26 = 64 smaller interval “t” (t =

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.

The 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”)

Low-order 6-bit data of DA register (DL)

Smaller intervals that HIGH duration is longer by

tm (m = “0” to “63”)

Nothing

m = 32

m = 16, 48

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

m = 2, 6, 10, 14, 18, ... 46, 50, 54, 58, 62

m = 1, 3, 5, 7, 9 ... 55, 57, 59, 61, 63

m = 1, 3, 5, 7, 9 ... 52, 55, 57, 59, 60, 61, 63

m = 1 to 63 (“0” is not included)

Number

MSB

0 0 0 0 0 0

LSB

0 0 0 0 0 1

0 0 0 0 1 0

0 0 0 0 1 1

0 0 0 1 0 0

0 0 0 1 0 1

0 0 0 1 1 0

0 0 1 0 0 0

0 1 0 0 0 0

1 0 0 0 0 0

1 0 1 0 0 0

1 1 1 1 1 1

FUNCTIONAL DESCRIPTION

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