XR16L580_07 Datasheet, PDF (10/52 Pages) Exar Corporation – SMALLEST 2.25V TO 5.5V UART WITH 16-BYTE FIFO AND POWERSAVE

XR16L580
SMALLEST 2.25V TO 5.5V UART WITH 16-BYTE FIFO AND POWERSAVE
REV. 1.4.1
TABLE 2: INT (IRQ#) PIN OPERATION FOR RECEIVER
INT Pin
(16/68# = 1)
IRQ# Pin
(16/68# = 0)
FCR BIT-0 = 0
(FIFO DISABLED)
0 = no data
1 = 1 byte
1 = no data
0 = 1 byte
FCR BIT-0 = 1
(FIFO ENABLED)
0 = FIFO below trigger level
1 = FIFO above trigger level
1 = FIFO below trigger level
0 = FIFO above trigger level
2.8 Crystal or External Clock Input
The L580 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. 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 voltage at the pin
should be VCC when an external clock is supplied. For programming details, see “Programmable Baud Rate
Generator.”
FIGURE 5. TYPICAL CRYSTAL CONNECTIONS
XTAL1
C1
22-47pF
XTAL2
R2
500K - 1M
R1
0-120
(Optional)
Y1
1.8432 MHz
to
24 MHz
C2
22-47pF
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 5). When VCC = 5V, the on-
chip oscillator can operate with a crystal whose frequency is not greater than 24 MHz. On the other hand, the
L580 can accept an external clock of up to 50MHz at XTAL1 pin, with a 2K ohms pull-up resistor on XTAL2 pin
(as shown in Figure 6). This translates to a maximum of 3.125Mbps serial data rate at 5V.
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