
181
8.4 Registers of 8/16-bit Capture Timer/Counter
8.4.5
Timer 0 Data Register (TDR0)
The timer 0 data register (TDR0) is used to set the timer 0 value in the 8-bit mode of the
8/16-bit capture timer/counter or the interval timer value (interval timer function) or
counter value (counter function) of the lower 8 bits in 16-bit mode.
s Timer 0 Data Register (TDR0)
The values set in this register are compared with those set in the counter.
Figure 8.4-6 "Bit
Structure of Timer 0 Data Register (TDR0)" shows the bit structure of timer 0 data register
(TDR0).
Figure 8.4-6 Bit Structure of Timer 0 Data Register (TDR0)
r 8-bit mode (timer 0)
The values set in this register are compared with those set in the counter. When the interval
timer function is used, an interval timer value is set. When the counter function is used, the
count value to be detected is set. When the count operation is allowed (TCR0: TSTR0 = 0 -->
1), the value in TDR0 is set in (loaded to) the comparator data latch and the counter is
incremented.
When the values in the comparator data latch match those in the counter as a result of the
increment, the values in the TDR0 are reset in the comparator data latch, the counter is cleared,
and the count operation is continued.
The comparator data latch is reset when a match is detected, thus, the values written to the
TDR0 when the counter is in operation become valid from the next cycle (after match detection).
Tip:
The values set in TDR0 when the interval timer is in operation can be calculated from the
expression shown below. However, the instruction cycle is affected by the clock mode and
gear function.
Values set in TDR0 = interval time/(count clock cycle x instruction cycle) - 1
r 16-bit mode
The values in TDR0 are compared with the counter values in the lower 8 bits of the 16-bit timer.
When the interval timer function is used, the lower 8 bits of the interval time are set. When the
counter function is used, the lower 8 bits of the count value to be detected are set. The values
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
R/W
R/W : Readable and Writable
X
: Undefined
Address
Initial value
001DH
XXXXXXXXB