XR16L580 Exar Corporation, XR16L580 Datasheet - Page 9

• Manufacturer Part Number: XR16L580
• Description: Smallest 2.25 to 5.5V Uart With 16-Byte Fifo And Power-save
• Manufacturer: Exar Corporation

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REV. 1.2.0
For further reading on the oscillator circuit please see the Application Note DAN108 on the EXAR web site at
http://www.exar.com.
The L580 UART has its own Baud Rate Generator (BRG) with a prescaler. The prescaler is controlled by a
software bit (bit-7) in the MCR register. This bit selects the prescaler to divide the input crystal or external clock
by a factor of 1 or 4. The clock output of the prescaler goes to the BRG. The BRG further divides this clock by
a programmable divisor (via DLL and DLM registers) between 1 and (2
clock of the serial data rate. The sampling rate clock is used by the transmitter for data bit shifting and receiver
for data sampling. The BRG divisor defaults to the maximum baud rate (DLL = 0x01 and DLM = 0x00) upon
power up.
Programming the Baud Rate Generator Registers DLM and DLL provides the capability of selecting the
operating data rate.
clock at 16X sampling rate clock rate. When using a non-standard data rate crystal or external clock, the
divisor value can be calculated for DLL/DLM with the following equation.
2.9
Programmable Baud Rate Generator
F
IGURE
X T A L 1
X T A L 2
divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16)
Table 3
6. B
AUD
shows the standard data rates available with a 14.7456 MHz crystal or external
R
C rysta l
B u ffe r
O sc/
ATE
SMALLEST 2.25V TO 5.5V UART WITH 16-BYTE FIFO AND POWERSAVE
F
IGURE
G
v c c
g n d
ENERATOR AND
5. E
E x te r n a l C lo c k
D ivid e b y 4
D ivid e b y 1
XTERNAL
P re sca le r
P re sca le r
R 1
2 K
V C C
P
9
RESCALER
C
LOCK
M C R B it-7 = 0
M C R B it-7 = 1
(d e fa u lt)
X T A L 1
X T A L 2
C
ONNECTION FOR
B a u d R a te
D L L a n d D L M
G e n e ra to r
R e g iste rs
L o g ic
16
-1) to obtain a 16X sampling rate
E
R a te C lo ck to
XTENDED
T ra n sm itte r
S a m p lin g
1 6 X
D
ATA
R
XR16L580
ATE