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III PERIPHERAL BLOCK: PRESCALER
S1C33L03 FUNCTION PART EPSON B-III-2-1
A-1
B-III
PSC
III-2 PRESCALER
Configuration of Prescaler
The prescaler divides the source clock (OSC3/PLL output clock or OSC1 clock) to generate the clocks for the
internal peripheral circuits. The prescaler division ratio can be selected for each peripheral circuit in a program. A
clock control circuit to control the clock supply to each peripheral circuit is also included.
The following are the peripheral circuits that use the output clock:
• 16-bit programmable timers 5 to 0 (and watchdog timer)
• 8-bit programmable timers 5 to 0 (and serial interface)
• A/D converter
Figure 2.1 shows the configuration of the prescaler.
For details on control of each peripheral circuit, refer to each corresponding section in this manual.
Division ratio
select register
Selector
Selector
1/21/1 1/4 1/8 1/16 1/32 1/64 1/128 1/256 1/512 1/1024 1/2048 1/4096
Control register
PSCON
θ
OSC3 or
PLL output clock
OSC1 clock
16-bit programmable timer 5–0
Prescaler
output control
8-bit programmable timer 5–0
A/D converter
Figure 2.1 Configuration of Prescaler and Clock Control Circuit
Source Clock
The source clock for the prescaler can be selected using PSCDT0 (D0) / Prescaler clock select register (0x40181).
When PSCDT0 = "0", the OSC3 clock (when the PLL is not used) or the PLL output clock (when the PLL is used)
is selected.
When PSCDT0 = "1", the OSC1 clock (typ. 32 kHz) is selected.
At initial reset, the OSC3/PLL output clock is selected.
Note: For the prescaler clock, the clock source same as the CPU operating clock must be selected.
For details on how to control the oscillation circuit and CPU operating clock, refer to "CLG (Clock Generator)".
At initial reset, the OSC3 clock is selected.
The source clock is supplied to the prescaler by writing "1" to PSCON (D5) / Power control register (0x40180). At
initial reset, PSCON is set to "1", so the prescaler is in an operating state. If all of said peripheral circuits can be
turned off and the peripheral circuits (e.g., 16-bit programmable timers (watchdog timer), 8-bit programmable
timers (DRAM refresh), A/D converter, serial interface, and ports) that use the prescaler input clock (the source
clock for prescaler) can be turned off, stop the prescaler by writing "0" to PSCON. This helps to reduce current
consumption.