C8051T630 Datasheet, PDF (106/221 Pages) Silicon Laboratories – Mixed-Signal Byte-Programmable EPROM MCU

C8051T630/1/2/3/4/5
19.4. External Oscillator Drive Circuit
The external oscillator circuit may drive an external capacitor or RC network. A CMOS clock may also pro-
vide a clock input. In RC, capacitor, or CMOS clock configuration, the clock source should be wired to the
EXTCLK pin as shown in Figure 19.1. The type of external oscillator must be selected in the OSCXCN reg-
ister, and the frequency control bits (XFCN) must be selected appropriately (see SFR Definition 19.5).
Important Note on External Oscillator Usage: Port pins must be configured when using the external
oscillator circuit. When the external oscillator drive circuit is enabled in capacitor, RC, or CMOS clock
mode, Port pin P0.3 is used as EXTCLK. The Port I/O Crossbar should be configured to skip the Port pin
used by the oscillator circuit; see Section “20.3. Priority Crossbar Decoder” on page 114 for Crossbar con-
figuration. Additionally, when using the external oscillator circuit in capacitor or RC mode, the associated
Port pin should be configured as an analog input. In CMOS clock mode, the associated pin should be
configured as a digital input. See Section “20.4. Port I/O Initialization” on page 116 for details on Port
input mode selection.
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