ST16C2552IJ 查看數據表（PDF） - Exar Corporation

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ST16C2552IJ

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

Exar Corporation 

ST16C2552

REV. 4.2.2

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

2.7 INTA and INTB Ouputs

The INTA and INTB interrupt outputs change according to the operating mode and enahnced features setup.

Tables 3 and 4 summarize the operating behavior for the transmitter and receiver. Also see Figures 16

through 21.

TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER

FCR BIT-0 = 0

(FIFO DISABLED)

INTA/B Pin 0 = a byte in THR

1 = THR empty

FCR BIT-0 = 1

(FIFO ENABLED)

0 = at least 1 byte in FIFO

1 = FIFO empty

TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER

FCR BIT-0 = 0

(FIFO DISABLED)

INTA/B Pin 0 = no data

1 = 1 byte

FCR BIT-0 = 1

(FIFO ENABLED)

0 = FIFO below trigger level

1 = FIFO above trigger level

2.8 Crystal Oscillator or Ext. Clock Input

The 2552 includes an on-chip oscillator (XTAL1 and XTAL2) to produce a clock for both UART sections in the

device. The CPU data bus does not require this clock for bus operation. The crystal oscillator provides a

system clock to the Baud Rate Generators (BRG) section found in each of the UART. XTAL1 is the input to the

oscillator or external clock buffer input with XTAL2 pin being the output. SEE”PROGRAMMABLE BAUD

RATE GENERATOR” ON PAGE 10.

FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS

XTAL1

XTAL2

R2

500 ΚΩ − 1 ΜΩ

R1

0-120 Ω

(Optional)

C1

22-47 pF

Y1

1.8432 MHz

to

24 MHz

C2

22-47 pF

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 Figure 2), with an external 500kΩ to

1 MΩ resistor across it. Alternatively, an external 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 Figure 4. For

further reading on oscillator circuit please see application note DAN108 on EXAR’s web site.

9

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