cop8tab5 National Semiconductor Corporation, cop8tab5 Datasheet - Page 17

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

10.0 Functional Description
10.6.3 External Oscillator
The External Oscillator mode can be selected by program-
ming Option Bit 3 to 0 and Option Bit 4 to 0. CKI can be
driven by an external clock signal provided it meets the
specified duty cycle, rise and fall times, and input levels.
G7/CKO is available as a general purpose input G7 and/or
Halt control. Figure 13 shows the external oscillator connec-
tion diagram.
10.6.4 Clock Prescaler
The device is equipped with a programmable clock prescaler
which allows the user to dynamically adjust the clock speed,
and thus the power dissipation, to the processing needs of
the application. By merely writing an eight-bit value to the
With External Frequency Control Resistor (R/C+R)
With On-Chip Bias Resistor
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FIGURE 13. External Oscillator
FIGURE 12. Crystal Oscillator
(Continued)
FIGURE 14. R/C Oscillator
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CLKPS register, the user can divide the input oscillator clock
by an integer multiple (1 — 256) and reduce the CPU clock
frequency. The format of the CLKPS Register is shown in
Table 5. The value written to the CLKPS register is one less
than the desired divider. A value of 0 (zero) written to the
CLKPS register yields a CPU clock equal to the input clock
frequency. A value of 255 written to the CLKPS register
yields a CPU clock with a period equal to 256 input clock
periods.
Bit 7
TABLE 5. Clock Prescale Register (CLKPS)
With Fully On-Chip R/C Oscillator.
With External Bias Resistor
CLKPS
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Bit 0