ST16C2552 データシートの表示（PDF） - Exar Corporation

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ST16C2552

2.97V TO 5.5V DUAL UART WITH 16-BYTE FIFO

Exar Corporation 

ST16C2552

2.97V TO 5.5V DUAL UART WITH 16-BYTE FIFO

REV. 4.2.2

2.9 Programmable Baud Rate Generator

A single baud rate generator 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 Figure 5) it can extend its operation up to 64 MHz (4Mbps serial data rate) at room temperature and

5.0V.

FIGURE 5. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE

External Clock

vcc

gnd

VCC

R1

2K

XTAL1

XTAL2

To obtain maximum data rate, it is necessary to use full rail swing on the clock input. See external clock

operating frequency over power supply voltage chart in Figure 6.

FIGURE 6. OPERATING FREQUENCY CHART. REQUIRES A 2K OHMS PULL-UP RESISTOR ON XTAL2 PIN TO INCREASE

OPERATING SPEED.

Operating frequency for ST16C2550

with external clock and a 2K ohms

pull-up resistor on XTAL2 pin.

80

-40oC

70

25oC

85oC

60

50

40

30

3.0 3.5 4.0 4.5 5.0 5.5

Suppy Voltage

The 2552 divides the basic external clock by 16. The basic 16X clock provides table rates to support standard

and custom applications using the same system design. The Baud Rate Generator divides this 16X clock by

any divisor from 1 to 216 -1. The rate table is configured via the DLL and DLM internal register functions.

Customized Baud Rates can be achieved by selecting the proper divisor values for the MSB and LSB sections

of baud rate generator.

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