ST16C1450CJ28 EXAR [Exar Corporation], ST16C1450CJ28 Datasheet - Page 8

• Manufacturer Part Number: ST16C1450CJ28
• Description: 2.97V TO 5.5V UART
• Manufacturer: EXAR [Exar Corporation]

ST16C1450/51
2.97V TO 5.5V UART
The 145X includes an on-chip oscillator (XTAL1 and XTAL2). The crystal oscillator provides the system clock to
the Baud Rate Generators (BRG) in the UART. XTAL1 is the input to the oscillator or external clock buffer input
with XTAL2 pin being the output. For programming details, see
Generator” on page
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant,
fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see
clock can be connected to the XTAL1 pin to clock the internal baud rate generator for standard or custom rates.
Typical oscillator connections are shown in
application note DAN108 on EXAR’s web site.
The UART has its own Baud Rate Generator (BRG). The BRG divides the input crystal or external clock by a
programmable divisor between 1 and (2
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 or a reset. Therefore, the BRG must be
programmed during initialization to the operating data rate. Programming the Baud Rate Generator Registers
DLM and DLL provides the capability of selecting the operating data rate.
rates available with a 14.7456 MHz crystal or external clock at 16X 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.
2.2
2.3
Crystal Oscillator or External Clock
Programmable Baud Rate Generator
divisor (decimal) = (XTAL1 clock frequency) / (serial data rate x 16)
8.
F
IGURE
22-47pF
XTAL1
16
4. T
C1
-1) to obtain a 16X sampling clock of the serial data rate. The
Figure
YPICAL OSCILLATOR CONNECTIONS
500K - 1M
R2
4. For further reading on oscillator circuit please see
22-47pF
8
XTAL2
C2
Y1
1.8432 MHz
(Optional)
24 MHz
0-120
R1
to
“Section 2.3, Programmable Baud Rate
Figure
Table 1
4). Alternatively, an external
shows the standard data
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REV. 4.2.0