User`s guide

1/15/03 2-1
Chapter 2
System Clocking
2.1 Theory of Operation
System clocking in the LZ87010 is provided by two sets of clock inputs: high-frequency
inputs XTAL1 and XTAL2, and low-frequency subclock inputs XTAL_SUB1 and
XTAL_SUB2. These inputs can be used either with crystal oscillators or external clock
generators, as shown in Figure 2-1.
The high-frequency oscillator operation is guaranteed from 20 MHz to 40 MHz. The low-
frequency oscillator is optimized for 32.768 kHz.
The oscillator circuit operates in Active and Standby modes, but in Stop mode the oscillator
is disabled. This means that Stop mode must be exited through a valid reset sequence,
and the oscillators must be given time to achieve stability before the reset is concluded.
Figure 2-1. System Oscillator Alternatives
XTAL2
39 pF
39 pF
27 pF
27 pF
32.768 kHz
22M
XTAL1
XTAL_SUB2
LZ87010
XTAL_SUB1
LZ87010-74
XTAL2
XTAL1
XTAL_SUB2
LZ87010
XTAL_SUB1
EXTERNAL
CLOCK
EXTERNAL
CLOCK
20-40 MHz