GMS77C1001 datasheet(33/44 Pages) HYNIX

33 / 44 page

GMS77C1000/GMS77C1001

July. 2001 Ver. 1.1

13. OSCILLATOR CIRCUITS

GMS77C100X supports four user-selectable oscillator

modes. The oscillator modes are selected by programming

the appropriate values into the configuration word.

- XT : Crystal/Resonator

- HF : High Speed Crystal/Resonator

- LF : Low Speed and Low Power Crystal

- RC : External Resistor/Capacitor

13.1 XT, HF or LF Mode

In XT, LF or HF modes, a crystal or ceramic resonator is

connected to the XIN and XOUT pins to establish oscillation

(Figure 13-1). The GMS77C100X oscillator design re-

quires the use of a parallel cut crystal. Use of a series cut

crystal may give a frequency out of the crystal manufactur-

ers specifications. Bits 0 and 1 of the configuration register

(FOSC1:FOSC2) are used to configure the different exter-

nal resonator/crystal oscillator modes. These bits allow the

selection of the appropriate gain setting for the internal

driver to match the desired operating frequency. When in

XT, LF or HF modes, the device can have an external clock

source drive the XIN pin (Figure 13-2). In this case, the

XOUT pin should be left open.

Note: These values are for design guidance only. Since

each resonator has its own characteristics, the user

should consult the resonator manufacturer for ap-

propriate values of external components.

Note: These values are for design guidance only. Since

each crystal has its own characteristics, the user

should consult the crystal manufacturer for appropri-

ate values of external components.

If you change from this device to another device,

please verify oscillator characteristics in your

application.

13.2 RC Oscillation Mode

The external RC oscillator mode provides a cost-effective

approach for applications that do not require a precise op-

erating frequency. In this mode, the RC oscillator frequen-

FIGURE 13-1 CRYSTAL OR CERAMIC RESONATOR

(HF, XT OR LF OSC CONFIGURATION)

FIGURE 13-2 EXTERNAL CLOCK INPUT OPERATION

(HF, XT OR LF OSC CONFIGURATION)

XOUT

XIN

To internal

RF(2)

SLEEP

logic

XTAL

C2(1)

C1(1)

Note 1: See Capacitor Selection tables for recommended

values of C1 and C2.

2: RF varies with the crystal chosen

(approx. value = 9 M

Ω).

XOUT

XIN

OPEN

GMS77C100X

Clock from

ext. system

Osc

Type

Resonator

Freq

Cap.Range

Cap. Range

455 kHz

2.0 MHz

4.0 MHz

22-100 pF

15-68 pF

22-100 pF

15-68 pF

4.0 MHz

8.0 MHz

16.0 MHz

15-68 pF

10-68 pF

10-22 pF

15-68 pF

10-68 pF

10-22 pF

TABLE 13-1 CAPACITOR SELECTION FOR CERAMIC

RESONATORS

Osc

Type

Crystal

Freq

Cap.Range

Cap. Range

32 kHz1

100 kHz

200 kHZ

For VDD > 4.5V, C1 = C2

≈ 30 pF is recommended.

15 pF

15-30 pF

15 pF

30-47 pF

15-82 pF

100 kHz

200 kHz

455 kHz

1 MHz

2 MHz

4 MHz

15-30 pF

15-47 pF

200-300 pF

100-200 pF

15-100 pF

15-30 pF

15-47 pF

4 MHz

8 MHz

20 MHz

15-30 pF

TABLE 13-2 CAPACITOR SELECTION FOR CRYSTAL

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