
S1C88409 TECHNICAL MANUAL
EPSON
123
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (8-bit Programmable Timer)
5.13 8-bit Programmable Timer
5.13.1 Configuration of 8-bit
programmable timer
The S1C88409 has a built-in 8-bit programmable
timer. The timer consists of an 8-bit presettable
down counter, and can be used as 8 bits
× 1
channel of programmable timer.
Figure 5.13.1.1 shows the configuration of the 8-bit
programmable timer.
The serial interface uses the underflow signal of
the 8-bit programmable timer as the synchronous
clock, so programmable setting of the transfer rate
is possible.
5.13.2 Setting of input clock
The prescaler supplies the clocks to the timer. The
prescaler generates the clocks for the timer by
dividing the source clock supplied from the OSC3
oscillation circuit.
Note: The prescaler, which supplies the clock to
the 8-bit programmable timer, can operate
only when the OSC3 oscillation has been
set to ON. Be aware that the 8-bit program-
mable timer does not operate when the
OSC3 oscillation circuit has been turned off.
Division ratio of the prescaler can be individually
selected by software.
The division ratio can be selected from eight kinds
using the prescaler division ratio selection register
PST2.
Further, it is necessary to control the prescaler
output using the clock control register PRPRT2.
Refer to Section 5.5, "Prescaler and Clock Control
Circuit for Peripheral Circuits", or Section 5.13.6,
"I/O memory of 8-bit programmable timer", for
setting of the division ratio.
Data
bus
8-bit reload data register (RLD)
8-bit down counter
Control registers
Control circuit
Serial I/F
Data buffer (PTD)
Underflow
Reload
fOSC3
Clock
output
Underflow
interrupt
Interrupt circuit
Prescaler/clock
control circuit
Fig. 5.13.1.1 Configuration of 8-bit programmable timer