GMS77C1001 Datasheet, PDF (34/44 Pages) Hynix Semiconductor – 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS77C1000/GMS77C1001
cy is a function of the supply voltage, the resistor(R) and
capacitor(C) values, and the operating temperature.
In addition, the oscillator frequency will vary from unit to
unit due to normal manufacturing process variations. Fur-
thermore, the difference in lead frame capacitance between
package types also affects the oscillation frequency, espe-
cially for low C values. The external R and C component
tolerances contribute to oscillator frequency variation as
well.
The user also needs to take into account variation due to
tolerance of external R and C components used.
Figure 13-3 shows how the R is connected to the
GMS77C100X. For Rext values below 2.2 kΩ, the oscilla-
tor operation may become unstable, or stop completely.
For very high Rext values (e.g., 1 MΩ) the oscillator be-
comes sensitive to noise, humidity and leakage. Thus, we
recommend keeping Rext between 3 kΩ and 100 kΩ. Ta-
ble 13-3 shows recommended value of Rext and Cext.
Although the oscillator will operate with no external ca-
pacitor (Cext = 0 pF), it is recommend using values above
20 pF for noise and stability reasons. With no or small ex-
ternal capacitance, the oscillation frequency can vary dra-
matically due to changes in external capacitances, such as
PCB trace capacitance or package lead frame capacitance.
Cext
Rext
Average F_XIN @ 5V, 25°C
3.3K
0pF
5K
10K
100K
7.48MHz
6.36MHz
4.04MHz
529KHz
20pF
3.3K
5K
10K
100K
4.60MHz
3.62MHz
2.14MHz
249KHz
100pF
3.3K
5K
10K
100K
1.75MHz
1.31MHz
734KHz
80KHz
300pF
3.3K
5K
10K
100K
702KHz
510KHz
283KHz
30KHz
TABLE 13-3 RC OSCILLATION FREQUENCIES
The Electrical Specifications sections show R frequency
variation from part to part due to normal process variation.
Also, see the Electrical Specifications sections for variation of os-
cillator frequency due to VDD for given Rext/Cext values as well
as frequency variation due to operating temperature for given R,
C, and VDD values.
The oscillator frequency, divided by 4, is available on the
X_OUT pin, and can be used for test purposes or to synchro-
nize other logic.
V_DD
R_ext
C_ext
F_XIN/4
X_IN
N
X_OUT
Internal
Clock
FIGURE 13-3 RC OSCILLATION MODE
July. 2001 Ver. 1.1
31