Epson S1C63558 4.3.6 I/O memory of oscillation circuit, 4.3.7 Programming notes, OSCC: OSC3 oscillation control register (FF00H•D2)

CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Oscillation Circuit)

4.3.6 I/O memory of oscillation circuit

Table 4.3.6.1 shows the I/O address and the control bits for the oscillation circuit.

Table 4.3.6.1 Control bits of oscillation circuit

Address		Register							Comment
	D3	D2	D1	D0	Name	Init ∗ 1	1	0
	CLKCHG	OSCC	0	Dummy	CLKCHG	0	OSC3	OSC1	CPU clock switch
FF00H					OSCC	0	On	Off	OSC3 oscillation On/Off
	R/W		R	R/W	0 ∗ 3	– ∗ 2			Unused
					Dummy	0			General-purpose register

*1 Initial value at initial reset

*2 Not set in the circuit

*3 Constantly "0" when being read

OSCC: OSC3 oscillation control register (FF00H•D2)

Controls oscillation ON/OFF for the OSC3 oscillation circuit.

When "1" is written: OSC3 oscillation ON

When "0" is written: OSC3 oscillation OFF

Reading: Valid

When it is necessary to operate the CPU at high speed, set OSCC to "1". At other times, set it to "0" to reduce current consumption.

At initial reset, this register is set to "0".

CLKCHG: CPU system clock switching register (FF00H•D3)

The CPU's operation clock is selected with this register.

When "1" is written: OSC3 clock is selected

When "0" is written: OSC1 clock is selected

Reading: Valid

When the CPU clock is to be OSC3, set CLKCHG to "1"; for OSC1, set CLKCHG to "0".

After turning the OSC3 oscillation ON (OSCC = "1"), switching of the clock should be done after waiting 5 msec or more.

At initial reset, this register is set to "0".

4.3.7 Programming notes

(1)It takes at least 5 msec from the time the OSC3 oscillation circuit goes ON until the oscillation stabi- lizes. Consequently, when switching the CPU operation clock from OSC1 to OSC3, do this after a minimum of 5 msec have elapsed since the OSC3 oscillation went ON.

Further, the oscillation stabilization time varies depending on the external oscillator characteristics and conditions of use, so allow ample margin when setting the wait time.

(2)When switching the clock form OSC3 to OSC1, use a separate instruction for switching the OSC3 oscillation OFF. An error in the CPU operation can result if this processing is performed at the same time by the one instruction.

(3)The internal operating voltage of VD1 is fixed at 2.2 V. So it is not necessary to control the operating voltage regardless of the operating clock selected.

S1C63558 TECHNICAL MANUAL EPSON 27