MITSUBISHI MICROCOMPUTERS
M37274EFSP
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER
and ON-SCREEN DISPLAY CONTROLLER
PWM OUTPUT FUNCTION
(4) Operating of 14-bit PWM
As with 8-bit PWM, set the bit 0 of the PWM mode register 1 (ad-
dress 020A16) to “0” (at reset, bit 0 is already set to “0” automati-
cally), so that the PWM count source is supplied. Pin DA is also used
as port P03. Select output mode by setting bit 3 of the port P0 direc-
tion register. Next, select the output polarity by bit 3 of the PWM
mode register 1. Then, the 14-bit PWM outputs from the D-A output
pin by setting bit 1 of the PWM mode register 1 to “0” (at reset, this bit
already set to “0” automatically) to select the DA output.
The M37274EFSP is equipped with a 14-bit PWM (DA) seven 8-bit
PWMs (PWM0–PWM6). DA has a 14-bit resolution with the mini-
mum resolution bit width of 0.25 µs and a repeat period of
4096 ms (for f(XIN) = 8 MHz). PWM0–PWM6 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) .
Figure 22 shows the PWM block diagram. The PWM timing generat-
ing circuit applies individual control signals to PWM0–PWM6 using
f(XIN) divided by 2 as a reference signal.
The output example of the 14-bit PWM is shown in Figure 23.
The 14-bit PWM divides the data of the DA latch into the low-order 6
bits and the high-order 8 bits.
(1) Data Setting
When outputting DA, first set the high-order 8 bits to the DA-H regis-
The fundamental waveform is determined with the high-order 8-bit
data “DH.” A “H” level area with a length τ ✕ DH(“H” level area of
fundamental waveform) is output every short area of “t” = 256τ =
64 ms (τ is the minimum resolution bit width of 0.25 µs). The “H” level
area increase interval (tm) is determined with the low-order 6-bit data
“DL.” The “H” level are of smaller intervals “tm” shown in Table 6 is
longer by τ than that of other smaller intervals in PWM repeat period
“T” = 64t. Thus, a rectangular waveform with the different “H” width is
output from the D-A pin. 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 “H” output cannot be output, i. e. 256/
256.
ter (address 024016), then the low-order 6 bits to the DA-L register
(address 024116). When outputting PWM0–PWM6, set 8-bit output
data to the PWMi register (i means 0 to 6; addresses 020016 to
020616).
(2) Transmitting Data from Register to PWM circuit
Data transfer from the 8-bit PWM register to the 8-bit PWM circuit is
executed at writing data to the register.
The signal output from the 8-bit PWM output pin corresponds to the
contents of this register.
Also, data transfer from the DA register (addresses 024016 and
024116) to the 14-bit PWM circuit is executed at writing data to the
DA-L register (address 024116). Reading from the DA-H register (ad-
dress 024016) means reading this transferred data. Accordingly, it is
possible to confirm the data being output from the D-A output pin by
reading the DA register.
(5) Output after Reset
At reset, the output of ports P00–P02 and P04–P07 is in the high-
impedance state and the contents of the PWM register and the PWM
circuit are undefined. Note that after reset, the PWM output is unde-
fined until setting the PWM register.
(3) Operating of 8-bit PWM
The following explains PWM operation.
First, set the bit 0 of PWM mode register 1 (address 020A16) to “0”
(at reset, bit 0 is already set to “0” automatically), so that the PWM
count source is supplied.
PWM0–PWM3 are also used as pins P04–P07, PWM4–PWM6 are
also used as pins P00–P02, respectively. Set the corresponding bits
of the port P0 direction register to “1” (output mode). And select each
output polarity by bit 3 of PWM mode register 1 (address 020A16).
Then, set bits 7 to 0 of PWM mode register 2 to “1” (PWM output).
The PWM waveform is output from the PWM output pins by setting
these registers.
Figure 23 shows the 8-bit PWM timing. One cycle (T) is composed
8
of 256 (2 ) segments. The 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 20 (a). The 8-bit PWM outputs 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 23 (b). 256 kinds of output (HIGH area: 0/256 to 255/256) are
selected by changing the contents of the PWM register. A length of
entirely HIGH cannot be output, i.e. 256/256.
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RENESAS [ RENESAS TECHNOLOGY CORP ]
