GMS77C1001 Datasheet, PDF (33/44 Pages) Hynix Semiconductor – 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS77C1000/GMS77C1001
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 X_IN and X_OUT 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 X_IN pin (Figure 13-2). In this case, the
X_OUT pin should be left open.
C1⁽¹⁾
X_OUT
C2⁽¹⁾
XTAL
X_IN
RF⁽²⁾
SLEEP
To internal
logic
Note 1: See Capacitor Selection tables for recommended
values of C1 and C2.
2: RF varies with the crystal chosen
(approx. value = 9 MΩ).
FIGURE 13-1 CRYSTAL OR CERAMIC RESONATOR
(HF, XT OR LF OSC CONFIGURATION)
Clock from
ext. system
OPEN
XIN
GMS77C100X
X_OUT
FIGURE 13-2 EXTERNAL CLOCK INPUT OPERATION
(HF, XT OR LF OSC CONFIGURATION)
Osc
Type
XT
HF
Resonator
Freq
455 kHz
2.0 MHz
4.0 MHz
4.0 MHz
8.0 MHz
16.0 MHz
Cap.Range
C1
22-100 pF
15-68 pF
15-68 pF
15-68 pF
10-68 pF
10-22 pF
Cap. Range
C2
22-100 pF
15-68 pF
15-68 pF
15-68 pF
10-68 pF
10-22 pF
TABLE 13-1 CAPACITOR SELECTION FOR CERAMIC
RESONATORS
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.
Osc
Type
LF
XT
HF
Crystal
Freq
32 kHz¹
100 kHz
200 kHZ
100 kHz
200 kHz
455 kHz
1 MHz
2 MHz
4 MHz
4 MHz
8 MHz
20 MHz
Cap.Range
C1
15 pF
15-30 pF
15-30 pF
15-30 pF
15-30 pF
15-30 pF
15-30 pF
15-30 pF
15-47 pF
15-30 pF
15-30 pF
15-30 pF
Cap. Range
C2
15 pF
30-47 pF
15-82 pF
200-300 pF
100-200 pF
15-100 pF
15-30 pF
15-30 pF
15-47 pF
15-30 pF
15-30 pF
15-30 pF
TABLE 13-2 CAPACITOR SELECTION FOR CRYSTAL
1. For VDD > 4.5V, C1 = C2 ≈ 30 pF is recommended.
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-
30
July. 2001 Ver. 1.1