M37221M4H/M6H/M8H/MAH–XXXSP/FP M37221EASP/FP
8.7 PWM OUTPUT FUNCTION
8.7.4 Operating of 14-bit PWM
This microcomputer is equipped with two 14-bit PWM (DA) and six
8-bit PWMs (PWM0–PWM5). DA1 and DA2 have a 14-bit resolution
with the minimum resolution bit width of 0.25 µs and a repeat period
of 4096 µs (for f(XIN) = 8 MHz). PWM0–PWM7 have the same circuit
structure and an 8-bit resolution with minimum resolution bit width of
4 µs and repeat period of 1024 µs (for f(XIN) = 8 MHz).
As with 8-bit PWM, set the bit 0 of PWM output control register 1
(address 00D516) to “0” (at reset, bit 0 is already set to “0” automati-
cally), so that the PWM count source is supplied. Next, select the
output polarity by bit 2 of PWM output control register 2 (address
00D616). Then, the 14-bit PWM outputs from the D-A output pin by
setting bit 1 of PWM output control register 1 to “0” (at reset, this bit
already set to “0” automatically) to select the DA output.
Figure 8.7.1 shows the PWM block diagram. The PWM timing gen-
erating circuit applies individual control signals to DA and PWM0–
PWM5 using f(XIN) divided by 2 as a reference signal.
The output example of the 14-bit PWM is shown in Figure 8.7.3.
The 14-bit PWM divides the data of the DA latch into the low-order 6
bits and the high-order 8 bits.
8.7.1 Data Setting
The fundamental waveform is determined with the high-order 8-bit
data “DH.” A HIGH area with a length t ✕ DH (HIGH area of funda-
mental waveform) is output every short area of “t” = 256τ =
64 µs (τ is the minimum resolution bit width of 250 ns). The HIGH
level area increase interval (tm) is determined with the low-order 6-bit
data “DL.” The HIGH are of smaller intervals “tm” shown in Table 5 is
longer by t than that of other smaller intervals in PWM repeat period
“T” = 64t. Thus, a rectangular waveform with the different HIGH width
is output from the DA pins. Accordingly, the PWM output changes by
τ unit pulse width by changing the contents of the DA-H and DA-L
registers. A length of entirely HIGH cannot be output, i. e. 256/256.
When outputting DA, first set the high-order 8 bits to the DA-H regis-
ter (address 00CE16), then the low-order 6 bits to the DA-L register
(address 00CF16). When outputting PWM0–PWM5, set 8-bit output
data to the PWMi register (i means 0 to 5; addresses 00D016 to
00D416, 00F616).
8.7.2 Transferring Data from Registers to PWM
Circuit
Data transfer from the 8-bit PWM register to the 8-bit PWM circuit is
executed when writing data to the register.
The signal output from the 8-bit PWM output pin corresponds to the
contents of this register.
8.7.5 Output after Reset
Also, data transfer from the DA register (addresses 00CE16 and
00CF16) to the 14-bit PWM circuit is executed at writing data to the
DA-L register (address 00CF16). Reading from the DA-H register
(address 00CE16) means reading this transferred data. Accordingly,
it is possible to confirm the data being output from the DA output pin
by reading the DA register.
At reset, the output of ports P00–P05 are in the high-impedance state,
and the contents of the PWM register and the PWM circuit are unde-
fined. Note that after reset, the PWM output is undefined until setting
the PWM register.
8.7.3 Operating of 8-bit PWM
The following explains the PWM operation.
First, set bit 0 of PWM output control register 1 (address 00D516) to
“0” (at reset, bit 0 is already set to “0” automatically), so that the
PWM count source is supplied.
Table 8.7.1 Relation Between the Low-order 6-bit Data and High-
level Area Increase Interval
PWM0–PWM5 are also used as ports P00–P05, respectively. Set
Low-order 6 bits of Data
0 0 0 0 0L0SB
Area Longer by τ than That of Other tm (m = 0 to 63)
those of the port P0 direction register to “1.” And select each output
polarity by bit 3 of PWM output control register 2 (address 00D616).
Then, set bits 2 to 7 of PWM output control register 1 to “1” (PWM
output).
Nothing
0 0 0 0 0 1 m = 32
0 0 0 0 1 0 m = 16, 48
The PWM waveform is output from the PWM output pins by setting
these registers.
0 0 0 1 0 0 m = 8, 24, 40, 56
0 0 1 0 0 0 m = 4, 12, 20, 28, 36, 44, 52, 60
0 1 0 0 0 0 m = 2, 6, 10, 14, 18, 22, 26, 30, 34, 38, 42, 46, 50, 54, 58, 62
1 0 0 0 0 0 m = 1, 3, 5, 7, ................................. 57, 59, 61, 63
Figure 8.7.2 shows the 8-bit PWM timing. One cycle (T) is com-
8
posed of 256 (2 ) segments. 8 kinds of pulses, relative to the weight
of each bit (bits 0 to 7), are output inside the circuit during 1 cycle.
Refer to Figure 8.7.2 (a). The 8-bit PWM outputs a waveform which
is the logical sum (OR) of pulses corresponding to the contents of
bits 0 to 7 of the 8-bit PWM register. Several examples are shown in
Figure 8.7.2 (b). 256 kinds of output (HIGH area: 0/256 to 255/256)
are selected by changing the contents of the PWM register. An en-
tirely HIGH selection cannot be output, i.e. 256/256.
Rev.1.00 Oct 01, 2002 page 44 of 110
REJ03B0134-0100Z
RENESAS [ RENESAS TECHNOLOGY CORP ]
