M30218 Datasheet, PDF (85/179 Pages) Mitsubishi Electric Semiconductor – M30218 Group

Timer B
Mitsubishi microcomputers
M30218 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
(2) Event counter mode
In this mode, the timer counts an external signal or an internal timer's overflow. (See Table TA-2.) Figure
TA-5 shows the timer Bi mode register in event counter mode.
Table TA-2. Timer specifications in event counter mode
Item
Specification
Count source
Count operation
•External signals input to TBiIN pin
•Effective edge of count source can be a rising edge, a falling edge, or falling
and rising edges as selected by software
•Counts down
•When the timer underflows, it reloads the reload register contents before
continuing counting
Divide ratio
1/(n+1)
n : Set value
Count start condition
Count start flag is set (= 1)
Count stop condition
Count start flag is reset (= 0)
Interrupt request generation timing The timer underflows
TBiIN pin function
Count source input
Read from timer
Count value can be read out by reading timer Bi register
Write to timer
•When counting stopped
When a value is written to timer Bi register, it is written to both reload register and counter
•When counting in progress
When a value is written to timer Bi register, it is written to only reload register
(Transferred to counter at next reload time)
Timer Bi mode register
b7 b6 b5 b4 b3 b2 b1 b0
01
Symbol
Address
TBiMR(i=0 to 2) 039B16 to 039D16
When reset
00XX00002
Bit symbol
TMOD0
TMOD1
Bit name
Operation mode
select bit
MR0
Count polarity select
bit (Note 1)
MR1
Function
b1 b0
0 1 : Event counter mode
RW
b3 b2
0 0 : Counts external signal's falling edges
0 1 : Counts external signal's rising edges
1 0 : Counts external signal's falling and
rising edges
1 1 : Inhibited
MR2
MR3
TCK0
TCK1
0 (Fixed to “0” in event counter mode; i = 0)
Nothing is assigned (i = 1, 2).
In an attempt to write to this bit, write “0”. The value, if read,
turns out to be indeterminate.
Invalid in event counter mode.
In an attempt to write to this bit, write “0”. The value, if read in event
counter mode, turns out to be indeterminate.
Invalid in event counter mode.
Can be “0” or “1”.
Event clock select
0: Input from TBiIN pin (Note 4)
1: TBj overflow
(j = i-1; however, j = 2 when i = 0)
(Note 2)
(Note 3)
Note 1: Valid only when input from the TBiIN pin is selected as the event clock.
If timer's overflow is selected, this bit can be “0” or “1”.
Note 2: Timer B0.
Note 3: Timer B1, timer B2.
Note 4: Set the corresponding port direction register to “0”.
Figure TA-5. Timer Bi mode register in event counter mode
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