7733 Datasheet, PDF (197/940 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER

TIMER B
7.6 Clock timer
7.6 Clock timer
Timer B2 functions as a clock timer on the following condition (Refer to Table 7.6.1.):
q When the port-Xc selection bit (bit 4 at address 6C16) = “1”
q When the port-Xc selection bit = “0” and the timer B2 clock source selection bit (bit 1 at address 6D16)
= “1”
Figure 7.6.1 shows the structures of the timer B2 mode register and timer B2 register when a clock timer
is used.
Table 7.6.1 Specifications of clock timer
Item
Specifications
Count source
fc32 (Sub clock divided by 32: f(XCIN)/32), or Main clock divided by 32: f(XIN)/32)
Count operation
q Countdown
q At an underflow, the reload register’s contents is reloaded, and
counting is continued.
Division ratio
1
(n + 1)
n: Set value in the timer B2 register
Count start condition
When the count start flag is set to “1.”
Count stop condition
When the count start flag is cleared to “0.”
Interrupt request occurrence timing At an underflow
Pin TB2IN’s function
Programmable I/O port or φSUB output pin
Read from timer
A counter value can be read out by reading the timer B2 register.
Write to timer
s While counting is stopped
When a value is written to the timer B2 register, it is written to both
of the reload register and counter.
s While counting is in progress
When a value is written to the timer B2 register, it is written only
to the reload register. (Transferred to the counter at the next reload
time.)
Clocks fc32 and f(XCIN): Refer to chapter “14. CLOCK GENERATING CIRCUIT.”
Either of f(XCIN)/32 or f(XIN)/32 can be selected as the clock timer’s count source, fc32.
The way to generate f(XCIN)/32 is different from that for clocks whose source is the system clock (e.g.,
internal clock φ, clocks f2 to f512, and so on). (Refer to chapter “14. CLOCK GENERATING CIRCUIT.”)
f(XCIN)/32 is not affected by the system clock selection bit and system clock stop bit at wait state (bits 3
and 5 at address 6C16). Therefore, in the wait mode, (Refer to chapter “11. STOP AND WAIT MODES.”)
only the clock timer can operate by itself. In other words, it is possible to supply fc32 only.
Oppositely, the way to generate f(XIN)/32 is the same as that for the system clock. Therefore, when the
system clock stop bit at wait state = “1,” fc32 is not supplied in the wait mode.
Figure 7.6.2 shows the structure of the clock timer.
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7733 Group User’s Manual