Rabbit 6000 User’s Manual
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18
2.2 Dependencies
2.2.1 I/O Pins
The main, Wi-Fi, Ethernet, and USB clocks contain a bypassable internal oscillator, so either a crystal or an
external clock input can be used. The selection of a crystal or an external signal for the main oscillator is
determined by the state of the CFG pins on startup, and by the Master System Status Register (MSSR). The
Ethernet clock source (main clock or PHY oscillator) is selected in the Master System Configuration Reg-
ister (MSCR). Table 2-1 lists the pins assigned to each clock and how they are controlled.
The 32 kHz clock input is on the CLK_32K pin. There is an internal Schmitt trigger on this pin to reduce
sensitivity to noise.
The peripheral clock or peripheral clock divided by 2 may be optionally output on the CLK pin by
enabling it via bits 7–6 in GOCR.
Table 2-1. Clock Pin Assignments
Clock
Frequency
Crystal Pins
External Clock
Signal Pins
Crystal/External
Clock Selection by
Main Clock
24 –42 MHz
(crystal)
20–200 MHz
(external
clock)
CLK_HSI
CLK_HSO
CLK_HSO
CFG pins
(see chapter 3)
W-Fi Clock
20 MHz
XTL_20MI
XTL_20MO
XTL_20MO
MSSR
Ethernet Clock
25 MHz
XTL_25MI
XTL_25MO
XTL_25MO
—
USB Clock
48 MHz
XTL_48MI
XTL_48MO
XTL_48MO
MSSR
32 kHz Clock
32 kHz
—
CLK_32K
—
Summary of Contents for 6000
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