ST16C2450CJ44 Просмотр технического описания (PDF) - Exar Corporation

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ST16C2450CJ44

2.97V TO 5.5V DUART

Exar Corporation 

xr

REV. 4.0.1

ST16C2450

2.97V TO 5.5V DUART

2.5 INTA and INTB Outputs

The INTA and INTB interrupt output changes according to the operating mode and enhanced features setup.

Table 2 summarizes the operating behavior for the transmitter and receiver. Also see Figure 12 and Figure 13.

INTA/B Pin

TABLE 2: INTA AND INTB PINS OPERATION FOR TRANSMITTER

TRANSMITTER

RECEIVER

0 = a byte in THR

1 = THR empty

0 = no data

1 = 1 byte

2.6 Crystal Oscillator or External Clock Input

The 2450 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 8.

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 100 ppm frequency

tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4), with an external 500 kΩ 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.

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