cop8tab5 National Semiconductor Corporation, cop8tab5 Datasheet - Page 16

• Manufacturer Part Number: cop8tab5
• Description: 8-bit Cmos Rom Microcontroller With 2k Or 4k Memory
• Manufacturer: National Semiconductor Corporation

www.national.com
10.0 Functional Description
The contents of data registers and RAM are unknown fol-
lowing the on-chip reset.
10.6 OSCILLATOR CIRCUITS
There are five clock oscillator options available: Crystal Os-
cillator with or without on-chip bias resistor, fully internal R/C
Oscillator, R/C Oscillator with external frequency determina-
tion resistor and External Oscillator. The oscillator feature is
selected by programming the Option Byte, which is summa-
rized in Table 2 .
(Continued)
FIGURE 11. Reset Timing (Power-On Reset Enabled)
Option
Byte 6
0
0
0
0
1
block that the system designer must address to properly recover from
a brownout condition. This is true regardless of whether the internal
POR or the external reset feature is used.
A brownout condition is reached when V
the minimum operating conditions of the device. The minimum guar-
anteed operating conditions are defined in the Electrical Specifica-
tions.
When using either the external reset or the POR feature to recover
from a brownout condition, external reset must be applied whenever
V
CC
goes below the minimum operating conditions as stated above.
Option
Byte 4
0
0
1
1
x
TABLE 2. Oscillator Option
with V
Option
Byte 3
0
1
0
1
x
CC
Tied to RESET
On-Chip R/C Oscillator
R/C Oscillator with External Resistor
Crystal Oscillator without Bias
Resistor
Crystal Oscillator with Bias Resistor
External Oscillator
Oscillator Option
CC
of the device goes below
20091723
16
10.6.1 Crystal Oscillator
The crystal Oscillator mode can be selected by programming
Option Bit 4 to 1. CKI is the clock input while G7/CKO is the
clock generator output to the crystal. An on-chip bias resistor
connected between CKI and CKO can be enabled by pro-
gramming Option Byte Bit 3 to 1 with the crystal oscillator
option selection. The value of the resistor is in the range of
0.3M to 2.5M (typically 1.0M). Table 3 shows the component
values required for various standard crystal values. Resistor
R2 is only used when the on-chip bias resistor is disabled.
Figure 12 shows the crystal oscillator connection diagram.
10.6.2 R/C Oscillator
The device features an R/C oscillator with two modes of
operation:
1. 1. R/C with internal R operaing at a fixed frequency (R/C
2. 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 R/C Oscillator mode will
be selected. In R/C oscillation mode, CKI is left floating,
while G7/CKO is available as a general purpose input G7
and/or HALT control. The R/C controlled oscillator has on-
chip resistor and capacitor for maximum R/C oscillator fre-
quency operation. The maximum frequency is 10 MHz
20% for temperature range of −40˚C to +85˚C.
The R/C Oscillator with external frequency control resistor
mode (R/C+R) can be selected by programming Option Byte
Bit 3 to 1 and Option Byte Bits 6 and 4 to 0. In R/C+R
oscillation mode, the frequency of oscillation is controlled by
the voltage across a resistor connected from the CKI pin to
GND. G7/CKO is available as a general purpose input G7
and/or HALT control. The maximum frequency is 10 MHz
20% for temperature range of −40˚C to +85˚C. For lower
frequencies, an external resistor should be connected be-
tween CKI and GND. PC board trace length on the CKI pin
should be kept as short as possible.
Table 4 shows the oscillator frequency as a function of
approximate external resistance on the CKI pin. Figure 14
shows the R/C oscillator configuration.
R1 (kΩ) R2 (MΩ) C1 (pF) C2 (pF)
External Resistor
5.6
mode)
mode).
0
0
0
TABLE 3. Crystal Oscillator Configuration,
TABLE 4. R/C Oscillator Configuration,
(kΩ)
200
500
56
87
OSC Freq. Variation of
1
1
1
1
T
A
−40˚C to +85˚C,
= 25˚C, V
100
18
18
45
R/C OSC Freq
100–156
(MHz)
30–36
15
10
5
2
CC
18
18
= 2.5V
±
CKI Freq. (MHz)
20%
Instr. Cycle
0.455
15
10
4
(µs)
0.65
1.0
2.0
5.0
±
±