Rainbow Electronics MAX3107 - Manual (Page 17)

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MAX3107
SPI/I
2
C UART with 128-Word FIFOs
and Internal Oscillator
Internal Oscillator
The internal 614.4kHz oscillator does not require exter-
nal components and provides a source for baud-rate
generation. The internal oscillator normally requires the
use of the internal PLL (see the PLL and Predivider sec-
tion) to achieve common baud rates. Set CLKSource[4]:
ExtClock to 0 and CLKSource[0]: IntOscEn to 1 to select
and enable the internal oscillator.
Crystal Oscillator
If a higher baud-rate accuracy or low-power consump-
tion is required, the crystal oscillator or an external clock
source can be used. Set CLKSource[4]: ExtClock to 1
and CLKSource[1]: CrystalEn to 1 to enable and select
the crystal oscillator. The on-chip crystal oscillator has
load capacitances of 20pF integrated in both XIN and
XOUT. Connect an external crystal or ceramic oscillator
between XIN and XOUT.
External Oscillator
When an external clock signal is used, this should
be connected to XIN. Leave XOUT unconnected.
Set CLKSource[4]: ExtClock to 1 and CLKSource[1]:
CrystalEn to 0 to select external clocking.
PLL and Predivider
The internal predivider and PLL allow for a wide range
of external clock frequencies and baud rates. The PLL
can be configured to multiply the input clock rate by a
factor of 6, 48, 96, or 144 through PLLConfig[7:6]. The
predivider, located between the input clock and the PLL,
allows division of the input clock by a factor between 1
and 63 by writing to PLLConfig[5:0]. See the PLLConfig
register description for more information.
Fractional Baud-Rate Generator
The internal fractional baud-rate generator provides a
high degree of flexibility and high resolution in baud-
rate programming. The baud-rate generator has a 16-bit
integer divisor and a 4-bit word for the fractional divisor.
The fractional baud-rate generator can be used either
with the internal oscillator or with the external crystal or
clock source.
Figure 6. Receive FIFO
Figure 7. Clock Selection Diagram
RECEIVE FIFO
FIFOTrgLvl[7:4]
TRIGGER
ISR[3]
WORD ERROR 128
RxFIFOLvl
4
3
2
1
TIMEOUT
EMPTY
ERRORS
OVERRUN
LSR[1]
RECEIVED
DATA
RHR
RECEIVER RX
I 2 C/SPI INTERFACE
LSR[0]
ISR[6]
LSR[5:2]
CURRENT FILL LEVEL
CRYSTAL
OSCILLATOR
XOUT
CrystalEn
IntOscEn
ExtClock
XIN
INTERNAL
OSCILLATOR
BAUD-RATE
GENERATOR
PLLByps
PLLEn
PLL DIVIDER