xr16l784iv Exar Corporation, xr16l784iv Datasheet - Page 8

• Manufacturer Part Number: xr16l784iv
• Description: High Performance 2.97v To 5.5v Quad Uart
• Manufacturer: Exar Corporation

XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
A single Baud Rate Generator (BRG) is provided for the transmitter and receiver, allowing independent TX/RX
channel control. The programmable Baud Rate Generator is capable of operating with a crystal frequency of
up to 24 MHz. However, with an external clock input on XTAL1 pin and a 2K ohms pull-up resistor on XTAL2
pin (as shown in
temperature and 5.0V.
F
Each UART has its own Baud Rate Generator (BRG) with a prescaler for the transmitter and receiver. The
prescaler is controlled by a software bit in the MCR register. The MCR register bit-7 sets the prescaler to divide
the input crystal or external clock by 1 or 4. The output of the prescaler clocks to the BRG. The BRG further
divides this clock by a programmable divisor between 1 and (2
the serial data rate. The sampling clock is used by the transmitter for data bit shifting and receiver for data
sampling. The BRG divisor (DLL and DLM registers) defaults to a random value upon power up. Therefore, the
BRG must be programmed during initialization to the operating data rate.
2.6
IGURE
4. E
Programmable Baud Rate Generator
XTERNAL
F
IGURE
XTAL1
XTAL2
Figure
5. B
C
LOCK
4) it can extend its operation up to 50 MHz (3.125 Mbps serial data rate) at room
AUD
C
Crystal
R
ONNECTION FOR
Buffer
Osc/
ATE
G
Channels
To Other
ENERATOR
vcc
gnd
External Clock
Divide by 4
Divide by 1
Prescaler
Prescaler
E
XTENDED
R1
2K
VCC
8
D
MCR Bit-7=1
MCR Bit-7=0
ATA
XTAL1
XTAL2
(default)
R
16
ATE
-1) to obtain a 16X or 8X sampling clock of
Baud Rate
DLL and DLM
Generator
Registers
Logic
Rate Clock to
and Receiver
Transmitter
16X or 8X
Sampling
xr
REV. 1.2.2