cop8tac9 National Semiconductor Corporation, cop8tac9 Datasheet - Page 19
cop8tac9
Manufacturer Part Number
cop8tac9
Description
8-bit Cmos Flash Microcontroller With 2k Byte Or 4k Byte Memory
Manufacturer
National Semiconductor Corporation
Datasheet
1.COP8TAC9.pdf
(59 pages)
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