XR19L402 datasheet(9/50 Pages) EXAR

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XR19L402

REV. 1.0.0

TWO CHANNEL INTEGRATED UART AND RS-485 TRANSCEIVER

Beyond the general 16C550 features and capabilities, the L402 offers enhanced feature registers just like the

XR16V2751, namely, EFR, Xon/Xoff 1, Xon/Xoff 2, FCTR, TRG, EMSR and FC that provide Xon/Xoff software

flow control, FIFO trigger level control and FIFO level counters. All the register functions are discussed in full

detail later in “Section 3.0, UART INTERNAL REGISTERS” on page 21.

2.7

INT (IRQ#) Output

The interrupt output changes according to the operating mode and enhanced features setup. Table 3 and

Table 4 below summarize the operating behavior for the transmitter and receiver in the Intel and Motorola

modes. Also see Figures 18 through 21.

TABLE 3: INT (IRQ#) PIN OPERATION FOR TRANSMITTER

FCR BIT-0 = 0 (FIFO DISABLED)

FCR BIT-0 = 1 (FIFO ENABLED)

INT Pin

(I/M# = 1)

0 = one byte in THR

1 = THR empty

0 = FIFO above trigger level

1 = FIFO below trigger level or FIFO empty

IRQ# Pin

(I/M# = 0)

1 = one byte in THR

0 = THR empty

1 = FIFO above trigger level

0 = FIFO below trigger level or FIFO empty

TABLE 4: INT (IRQ#) PIN OPERATION FOR RECEIVER

FCR BIT-0 = 0

(FIFO DISABLED)

FCR BIT-0 = 1

(FIFO ENABLED)

INT Pin

(I/M# = 1)

0 = no data

1 = 1 byte

0 = FIFO below trigger level

1 = FIFO above trigger level

IRQ# Pin

(I/M# = 0)

1 = no data

0 = 1 byte

1 = FIFO below trigger level

0 = FIFO above trigger level

2.8

Crystal or External Clock Input

The L402 includes an on-chip oscillator (XTAL1 and XTAL2) to generate a clock when a crystal is connected

between the XTAL1 and XTAL2 pins of the device. Alternatively, an external clock can be supplied through the

XTAL1 pin. 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 input and XTAL2 pin is the bufferred output which can be used as a clock signal for

other devices in the system. Please note that the input XTAL1 is not 5V tolerant and therefore, the maximum

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