7516 datasheet(46/90 Pages) RENESAS

46 / 90 page

Rev.1.01

Jul 01, 2003

page 46 of 89

7516 Group

CLOCK GENERATING CIRCUIT

The 7516 group has two built-in oscillation circuits: main clock XIN-

XOUT oscillation circuit and sub clock XCIN-XCOUT oscillation

circuit. An oscillation circuit can be formed by connecting a reso-

nator between XIN and XOUT (XCIN and XCOUT). Use the circuit

constants in accordance with the resonator manufacturer’s recom-

mended values. No external resistor is needed between XIN and

XOUT since a feed-back resistor exists on-chip. However, an exter-

nal feed-back resistor is needed between XCIN and XCOUT.

Immediately after power on, only the XIN oscillation circuit starts

oscillating, and XCIN and XCOUT pins function as I/O ports.

Frequency Control

(1) Middle-speed mode

The internal clock

φ is the frequency of XIN divided by 8. After re-

set is released, this mode is selected.

(2) High-speed mode

The internal clock

φ is half the frequency of XIN.

(3) Low-speed mode

The internal clock

φ is half the frequency of XCIN.

sNote

If you switch the mode between middle/high-speed and low-

speed, stabilize both XIN and XCIN oscillations. The sufficient time

is required for the sub-clock to stabilize, especially immediately af-

ter power on and at returning from the stop mode. When switching

the mode between middle/high-speed and low-speed, set the fre-

quency on condition that f(XIN) > 3•f(XCIN).

(4) Low power dissipation mode

The low power consumption operation can be realized by stopping

the main clock XIN in low-speed mode. To stop the main clock, set

bit 5 of the CPU mode register to “1.” When the main clock XIN is

restarted (by setting the main clock stop bit to “0”), set sufficient

time for oscillation to stabilize.

The sub-clock XCIN-XCOUT oscillation circuit can not directly input

clocks that are generated externally. Accordingly, make sure to

cause an external resonator to oscillate.

Oscillation Control

(1) Stop mode

If the STP instruction is executed, the internal clock

φ stops at an

“H” level, and XIN and XCIN oscillation stops. When the oscillation

stabilizing time set after STP instruction released bit is “0,” the

prescaler 12 is set to “FF16” and timer 1 is set to “0116.” When the

oscillation stabilizing time set after STP instruction released bit is

“1,” set the sufficient time for oscillation of used oscillator to stabi-

lize since nothing is set to the prescaler 12 and timer 1.

Either XIN or XCIN divided by 16 is input to the prescaler 12 as

count source. Oscillator restarts when an external interrupt is re-

ceived, but the internal clock

φ is not supplied to the CPU (remains

at “H”) until timer 1 underflows. The internal clock

φ is supplied for

the first time, when timer 1 underflows. This ensures time for the

clock oscillation using the ceramic resonators to be stabilized.

When the oscillator is restarted by reset, apply “L” level to the

Fig. 52 Ceramic resonator circuit

Fig. 53 External clock input circuit

RESET pin until the oscillation is stable since a wait time will not

be generated.

(2) Wait mode

If the WIT instruction is executed, the internal clock

φ stops at an

“H” level, but the oscillator does not stop. The internal clock

φ re-

starts at reset or when an interrupt is received. Since the oscillator

does not stop, normal operation can be started immediately after

the clock is restarted.

To ensure that the interrupts will be received to release the STP or

WIT state, their interrupt enable bits must be set to “1” before ex-

ecuting of the STP or WIT instruction.

When releasing the STP state, the prescaler 12 and timer 1 will

start counting the clock XIN divided by 16. Accordingly, set the

timer 1 interrupt enable bit to “0” before executing the STP instruc-

tion.

sNote

When using the oscillation stabilizing time set after STP instruction

released bit set to “1”, evaluate time to stabilize oscillation of the

used oscillator and set the value to the timer 1 and prescaler 12.

XCIN

XCOUT

XIN

XOUT

CIN

COUT

CCIN

CCOUT

XCIN

XCOUT

XIN

XOUT

CCIN

CCOUT

Open

External oscillation

circuit

Vcc

Vss

7516 Datasheet(PDF) 46 Page - Renesas Technology Corp

7516 Datasheet(HTML) 46 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

Datasheet Download

Link URL