SM5L1 데이터 시트보기 (PDF) - Sharp Electronics

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SM5L1

4-Bit Single Chip Microcomputers

Sharp Electronics 

SM5L1/SM5L2/SM5L3

4-Bit Single Chip Microcomputers

System Clock Generator and Dividers

The main oscillation frequency which is input

through OSCIN - OSCOUT or OSCIN - CK2 is divided

into two or four to generate the system clock fSYS. This

function is shown in Figure 19.

System clock fSYS determines the execution instruc-

tion cycle so that the system clock period is the same

as the instruction cycle.

However, the instruction execution cycle of two-

word instruction is twice that of one word instructions.

Use of a CR oscillating element or a crystal oscillating

element for the oscillator circuit is determined by the

mask option. The crystal oscillator which is input through

OSCIN - OSCOUT can be used as both real time clock

and display signal of LCD. On the final stage of the

divider, fc can be set to 1 Hz or 2 Hz (in case of 32 kHz

crystal oscillation) depending on the mask option.

Either of the system clock frequencies 16.384 kHz or

8.192 kHz (in case of 32.768 kHz oscillation) can be

selected by the RF2 flag (see Table 2). The 8.192 kHz

clock has slower command execution speed, but uses

less power for the same function.

The system clock is initialized to 16.384 kHz after

hardware reset operation.

Table 2 shows the relationship between the contents

of RF2 flag for the OSC resonator and the generated

frequency, fSYS.

Table 2. OSC Resonator and Frequency fSYS

FOR OSC RESONATOR CONTENTS OF RF2 FLAG

0

32.768 kHz crystal oscillation

1

GENERATED FREQUENCY fSYS

16.384 kHz

8.192 kHz

0

40 kHz CR oscillation

1

20 kHz

10 kHz

OSCIN

OSCOUT

CK2

OSC

OSCIN - OSCOUT: Crystal

oscillation (32.768 kHz)

or

OSCIN - CK2: CR

oscillation (40 kHz)

DIVIDER

f14 - - - - - - - - - - - - - - - - - - - - - - - - - - f0

4 kHz 2 kHz

256 Hz

1 Hz

fc

2 Hz

fc = 1 Hz or 2 Hz

Determined by

mask option

RF2

CG

MPX.

fSYS

fSYS = 8.192 kHz or

16.384 kHz (crystal oscillation) or

fSYS = 10 kHz or 20 kHz (CR oscillation)

5L1-19

Figure 19. System Clock Generator and Divider

14

Microcomputer Data Sheet

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