14 8-BIT TIMERS (T8)
14-4
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
Count clock
PRESER write
PRUN
Counter
Interrupt request
0
1
n-1
n
n
Count clock
PRESER write
PRUN
Counter
Interrupt request
0
1
n-1
n
n
0
1
n-1
n
n-1
One-shot mode
Repeat mode
Reset by hardware
Set by software
Set by software
Reset by software
6.1 Count Operation
Figure 14.
T8 Output Signals
14.7
T8 outputs underflow pulses when the counter underflows.
These pulses are used for timer interrupt requests.
These pulses are also used to generate the serial transfer clock for the internal serial interface or the A/D trigger sig-
nal.
The clock generated is sent to the internal peripheral module, as shown below.
T8 Ch.0 output clock
→
USI
T8 Ch.3 output clock
→
USIL
T8 Ch.2 output clock
→
A/D converter
Underflow signal
Timer output
(serial transfer clock, A/D trigger signal)
Interrupt request to the ITC
7.1 Timer Output Clock
Figure 14.
Fine Mode (Ch.0 to Ch.3)
14.8
Ch.0 to Ch.3 support fine mode to minimize transfer rate errors.
T8 can output a programmable clock signal for use as the USI serial transfer clock. The timer output clock can be
set to the required frequency by selecting the appropriate prescaler output clock and reload data. Note that errors
may occur, depending on the transfer rate. Fine mode extends the output clock cycle by delaying the underflow
pulse from the counter. This delay can be specified with the TFMD[3:0]/T8_CTL
x
register.
TFMD[3:0] specifies the delay pattern to be inserted into a 16 underflow period. Inserting one delay extends the
output clock cycle by one count clock cycle. This setting delays the interrupt timing in the same way.