GMS81C2020 Datasheet, PDF (48/92 Pages) Hynix Semiconductor – CMOS Single-Chip 8-Bit Microcontroller with A/D Converter & VFD Driver

GMS81C2020/GMS81C2120
Hyundai Micro Electro nics
13. CLOCK GENERATOR
The clock generator produces the basic clock pulses which
provide the system clock to be supplied to the CPU and pe-
ripheral hardware. The main system clock oscillator oscil-
lates with a crystal resonator or a ceramic resonator
CLKSEL
CS[1:0]
connected to the XI and XO pins. External clocks can be
input to the main system clock oscillator. In this case, input
a clock signal to the XI pin and open the XO pin.

OSCILLATION fXI
CIRCUIT
SUB
OSCILLATION
CIRCUIT
fSXI
0
1 _{fXI÷ 4}
fXI÷ 8
fXI÷32
MUX
CLOCK PULSE
GENERATOR
Internal system clock
STOP
WAKEUP
PRESCALER
÷1
÷2 ÷4 ÷8 ÷16 ÷32 ÷64 ÷128 ÷256 ÷512 ÷1024 ÷2048 ÷4096
Peripheral clock
System Clock Mode Register
SCMR
-
-
ADDRESS : FAH
-
CS1
CS0 SUBOFF CLKSEL MAINOFF
RESET VALUE : ---00000
CS[1:0]
SUBOFF
Clock selection enable bits
00 : fXI ÷ 210 : fXI ÷16
01 : fXI ÷ 811 : fXI ÷ 64
Sub clock control bit
0: On sub clock
1: Off sub clock
CLKSEL
Clock selection bit
0 : Main clock selection
1 : Sub clock selection
MAINOFF Main clock control bit
0: On main clock
1: Off main clock
Figure 13-1 Block Diagram of Clock Pulse Generator
13.1 Oscillation Circuit
XI and XO are the input and output, respectively, a invert-
ing amplifier which can be set for use as an on-chip oscil-
lator, as shown in Figure 13-2 .
XO
C1
C2
XI
Vss
Figure 13-2 Oscillator Connections
SXI and SXO are the input and output, respectively, a in-
verting amplifier which can be set for use as an on-chip os-
Recommended: C1, C2 = 30pF±10pF for Crystals
48
preliminary
Nov. 1999 Ver 0.0