XR16V794 Datasheet, PDF (7/53 Pages) Exar Corporation – HIGH PERFORMANCE 2.25V TO 3.6V QUAD UART WITH FRACTIONAL

XR16V794
REV. 1.0.0
HIGH PERFORMANCE 2.25V TO 3.6V QUAD UART WITH FRACTIONAL BAUD RATE
2.4 INT# Ouput
The INT# interrupt output changes according to the operating mode and enhanced features setup. Table 2
and 3 summarize the operating behavior for the transmitter and receiver.
TABLE 2: INT# PIN OPERATION FOR TRANSMITTER
Auto RS485
Mode
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1
(FIFO ENABLED)
NO
HIGH = a byte in THR HIGH = FIFO above trigger level
LOW = THR empty
LOW = FIFO below trigger level or FIFO empty
YES
HIGH = a byte in THR HIGH = FIFO above trigger level
LOW = transmitter empty LOW = FIFO below trigger level or transmitter empty
TABLE 3: INT# PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1
(FIFO ENABLED)
HIGH = no data
LOW = 1 byte
HIGH = FIFO below trigger level
LOW = FIFO above trigger level
2.5 CRYSTAL OSCILLATOR / BUFFER
The 794 includes an on-chip oscillator. The crystal oscillator provides the system clock to the Baud Rate
Generators (BRG) in each of the 4 UARTs, the 16-bit general purpose timer/counter and internal logics. XTAL1
is the input to the oscillator or external clock buffer input with XTAL2 pin being the output. For programming
details, see “Section 2.6, Programmable Baud Rate Generator with Fractional Divisor” on page 8.
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 3). Alternatively, an external
clock can be connected to the XTAL1 pin to clock the internal 4 baud rate generators for standard or custom
rates. The typical oscillator connections are shown in Figure 3. For further reading on oscillator circuit please
see application note DAN108 on EXAR’s web site.
FIGURE 3. TYPICAL OSCILLATOR CONNECTIONS
R=300K to 400K
XTAL1
XTAL2
24 MHz
C1
22-47pF
C2
22-47pF
7