at89lp216-20xi ATMEL Corporation, at89lp216-20xi Datasheet - Page 11

• Manufacturer Part Number: at89lp216-20xi
• Description: At89lp216 8-bit Microcontroller With 2k Bytes Flash
• Manufacturer: ATMEL Corporation

9. System Clock
9.1
9.2
9.3
9.4
3621B–MICRO–11/07
Crystal Oscillator
External Clock Source
Internal RC Oscillator
System Clock Out
The system clock is generated directly from one of three selectable clock sources. The three
sources are the on-chip crystal oscillator, external clock source, and internal RC oscillator. The
clock source is selected by the Clock Source User Fuses as shown in
clock division is used to generate the CPU clock from the system clock. See
Fuses” on page
Table 9-1.
When enabled, the internal inverting oscillator amplifier is connected between XTAL1 and
XTAL2 for connection to an external quartz crystal or ceramic resonator. When using the crystal
oscillator, P3.2 and P3.3 will have their inputs and outputs disabled. When using the crystal
oscillator, XTAL2 should not be used to drive a board-level clock without a buffer.
The external clock option disables the oscillator amplifier and allows XTAL1 to be driven directly
by the clock source. XTAL2 may be left unconnected, used as P3.3 I/O, or configured to output
a divided version of the system clock.
The AT89LP216 has an internal RC oscillator tuned to 8.0 MHz ±2.5%. When enabled
as the clock source, XTAL1 and XTAL2 may be used as P3.2 and P3.3 respectively. XTAL2
may also be configured to output a divided version of the system clock. The frequency of the
oscillator may be adjusted by changing the RC Adjust Fuses.
on page
When the AT89LP216 is configured to use either an external clock or the internal RC oscillator,
a divided version of the system clock may be output on XTAL2 (P3.3). The clock out feature is
enabled by setting the COE bit in CLKREG. The two CDV bits determine the clock divide ratio.
For example, setting COE = “1” and CDIV = “00” when using the internal oscillator will result in a
3.950 MHz (±5%) clock output on P3.3. P3.3 must be configured as an output in order to use the
clock out feature.
Clock Source
Fuse 1
71.).
0
0
1
1
Clock Source Settings
71.
Clock Source
Fuse 0
0
1
0
1
Selected Clock Source
Crystal Oscillator
Reserved
External Clock on XTAL1
Internal 8 MHz RC Oscillator
(See “User Configuration Fuses”
Table
AT89LP216
“User Configuration
9-1. No internal
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