Timer A
Mitsubishi microcomputers
M16C / 6K7 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
84
Rev.1.0
(4) Pulse width modulation (PWM) mode
In this mode, the timer outputs pulses of a given width in succession. (See Table.FB-5) In this mode, the
counter functions as either a 16-bit pulse width modulator or an 8-bit pulse width modulator. Fig.FB-11
shows the timer Ai mode register in pulse width modulation mode. Fig.FB-12 shows the example of how a
16-bit pulse width modulator operates. Fig.FB-13 shows the example of how an 8-bit pulse width modulator
operates.
Fig.FB-11 Timer Ai mode register in pulse width modulation mode
Table.FB-5 Timer specifications in pulse width modulation mode
Bit name
Timer Ai mode register
Symbol
Address
When reset
TAiMR(i=0 to 4)
039616 to 039A16
0016
Function
Bit symbol
b7
b6
b5
b4
b3
b2
b1
b0
Operation mode selection
bits
1 1 : PWM mode
b1 b0
TMOD1
TMOD0
MR0
MR2
MR1
MR3
0 0 : f1
0 1 : f8
1 0 : f32
1 1 : fC32
b7 b6
TCK1
TCK0
Count source selection bits
W
R
11
1
1 (Must always be “1” in PWM mode)
16/8-bit PWM mode
selection bit
0: Functions as a 16-bit pulse width modulator
1: Functions as an 8-bit pulse width modulator
Trigger selection bit
External trigger selection
bit (Note 1)
0: Falling edge of TAiIN pin's input signal (Note 2)
1: Rising edge of TAiIN pin's input signal (Note 2)
0: Count start flag is valid
1: Selected by event/trigger selection register
Note 1: Valid only when the TAiIN pin is selected by the event/trigger selection bit
(addresses 038216 and 038316). If timer overflow is selected, this bit can be “1” or “0”.
Note 2: Set the corresponding port direction register to “0”.
Item
Specification
Count source
f1, f8, f32, fC32
Count operation
The timer counts down (operating as an 8-bit or a 16-bit pulse width modulator)
The timer reloads a new count at a rising edge of PWM pulse and continues counting
The timer is not affected by a trigger that occurs when counting
16-bit PWM
High level width
n / fi
n : Set value
Cycle time
(216-1) / fi fixed
8-bit PWM
High level width n (m+1) / fi
n : values set to timer Ai register’s high-order address
Cycle time
(28-1) (m+1) / fi
m : values set to timer Ai register’s low-order address
Count start condition
External trigger is input
The timer overflows
The count start flag is set (= 1)
Count stop condition
The count start flag is reset (= 0)
Interrupt request generation timing
The falling edge of PWM pulse
TAiIN pin function
Programmable I/O port or trigger input
TAiOUT pin function
Pulse output
Read from timer
When timer Ai register is read, it indicates an indeterminate value
Write to timer
When counting stopped
When a value is written to timer Ai register, it is written to both reload
register and counter
When counting in progress
When a value is written to timer Ai register, it is written to only reload register
(Transferred to counter at next reload time)