cop8tac9 National Semiconductor Corporation, cop8tac9 Datasheet - Page 19

• Manufacturer Part Number: cop8tac9
• Description: 8-bit Cmos Flash Microcontroller With 2k Byte Or 4k Byte Memory
• Manufacturer: National Semiconductor Corporation

10.0 Functional Description
10.7 OSCILLATOR CIRCUITS
There are five clock oscillator options available: fully internal
R/C Oscillator, R/C Oscillator with external frequency deter-
mination resistor, Crystal Oscillator with or without on-chip
bias resistor and External Oscillator. The oscillator feature is
selected by programming the Option Byte, which is summa-
rized in Table 2.
(Continued)
FIGURE 13. Reset Timing (Power-On Reset Enabled)
Option
Bit 6
0
0
0
0
1
Option
Bit 4
0
0
1
1
x
TABLE 2. Oscillator Option
with V
Option
Bit 3
0
1
0
1
x
CC
Tied to RESET
On-Chip R/C Oscillator
R/C Oscillator with External Resistor
Crystal Oscillator with Internal Bias
Resistor
Crystal Oscillator with External Bias
Resistor
External Oscillator
Oscillator Option
20047523
19
10.7.1 R/C Oscillator
The device features an R/C oscillator with two modes of
operation:
1. R/C with internal R operating at a fixed frequency (R/C
2. R/C with external frequency control resistor (R/C+R
If the Oscillator Selection bits of the Option Byte remain
unprogrammed (equal to zero), the internal R/C Oscillator
mode will be selected. In internal R/C oscillation mode, CKI
may be left unconnected, while G7/CKO is available as a
general purpose input G7 and/or HALT control. The internal
R/C oscillator has on-chip resistor and capacitor for prede-
termined R/C oscillator frequency operation. The predeter-
mined frequency is 10 MHz
−40˚C to +85˚C.
The R/C Oscillator with external frequency control resistor
mode (R/C+R) can be selected by programming Option Bit 3
to 1 and Option Bits 6 and 4 to 0. In R/C+R mode, the
frequency of oscillation is controlled by the current through a
resistor connected from the CKI pin to GND. G7/CKO is
available as a general purpose input G7 and/or HALT con-
trol. The maximum frequency is 10 MHz
ture range of −40˚C to +85˚C. For lower frequencies, an
external resistor should be connected between CKI and
GND. PC board trace length on the CKI pin should be kept
as short as possible.
Table 3 shows the oscillator frequency as a function of
approximate external resistance on the CKI pin. Figure 17
shows the R/C oscillator configuration.
External Resistor
FIGURE 14. Crystal Oscillator With On-Chip Bias
mode)
mode).
TABLE 3. R/C+R Oscillator Configuration,
(kΩ)
100
200
500
60
OSC Freq. Variation of
−40˚C to +85˚C,
Resistor
OSC Freq
±
(MHz)
20% for temperature range of
15
10
5
2
20047524
±
±
20%
20% for tempera-
Instr. Cycle
0.65
www.national.com
(µs)
1.0
2.0
5.0