HD614P080S-------------------------------------------------------------
i--="-~-~
TCA(Bbit)
TIMER COUNTER A
INTERRUPT
REQUEST FLAG
OF
TlMER-A
Fig.
13 Timer/Counter Block Diagram
•
TIMER·A
Oper.tion
After TIMER·A
is
initialized to
SOO
by MeU reset, it counts
up
at
every clock input signal. When the next clock signal
is
applied after TIMER·A
is
counted up
to
SFF, TIMER·A
is
set
to
SOO
again, and generating overflow output. This leads to
setting
TIMER·A Interrupt Request Flag (IFTA:
SOOI,
2) to
"I".
Therefore, this timer can function as an interval timer
periodically generating overflow
output
at every 256th ,clock
signal input.
The clock input signals
to
TIMER·A are selected by the
Timer Mode Register A (TMA:
S008).
•
TIME
R·B
Opeqtion
Timer Mode Register B (TMB: S009)
is
used to select the
auto·reload function and the prescaler divide ratio
of
TIMER·B
as the input clock source. When the external event input
is
used
as
an input clock signal
to
TIMER·B, select the
R33
lINT I
as !NT I and set the External Interrupt
Mask
(1M
1) to
"I"
to
prevent the external interrupt request from occurring.
TIMER·B
is
initialized according
to
the value written into the
Timer Load Register by software.
TIMER·B counts up at every
clock input signal. When the next clock signal
is
applied to
TIMER·B after TIMER·B
is
set to SFF, TIMER·B will
be
initio
alized
again
and generate overflow output. In this case
if
the
auto-reload function
is
selected. TIMER·B
is
initialized accord·
ing to the value
of
the Timer Load Register. Else
if
the auto-
reload function is not selected, TIMER·B goes to
SOO.
TIMER·
B Interrupt Request Flag (IFTB: S002,O) will
be
set at this
overflow output.
• Timer Mode Register A (TMA: $008)
The Timer Mode Register A
is
a 3·bit write·only register.
The
TMA
controls the prescaler divide ratio
of
TIMER·A clock
input,
as
shown in Table
II.
The Timer Mode Register A
is
initialized to $0 by
MCU
reset.
• Timer Mode Register B (TMB: $009)
The Timer Mode Register B
is
a 4·bit write·only register. The
Timer Mode Register B controls the selection for the
auto-
reload function
of
TIMER·B and the pre scaler divide ratio,
and the source
of
the clock input signal,
as
shown in Table 12,
The Timer Mode Register B
is
initialized to $00 by
MCU
reset.
The operation mode
of
TIMER-B is changed
at
the second
instruction cycle after writing into the Timer Mode Register
B.
276
Therefore, it
is
necessary to program the write instruction
to
TLRU after the content
of
TMB
is
changed.
Table 11. Timer Mode Register A
TMA
Bit 2 Bit 1 BitO
Prescaler
Divide Ratio
0
0
0
+2048
0 0
1
+1024
0
1 0
+
512
0 1 1 128
1
0
0
32
1
0 1
8
1 1 0
4
1 1
1
2
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