XR16V2550 Datasheet, PDF (9/48 Pages) Exar Corporation – HIGH PERFORMANCE DUART WITH 16-BYTE FIFO

PRELIMINARY
XR16V2550
REV. P1.0.0
HIGH PERFORMANCE DUART WITH 16-BYTE FIFO
2.8 INTA and INTB Outputs
The INTA and INTB interrupt output changes according to the operating mode and enhanced features setup.
Table 3 and 4 summarize the operating behavior for the transmitter and receiver. Also see Figures 17
through 22.
TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1 (FIFO ENABLED)
INTA/B Pin
LOW = a byte in THR
HIGH = THR empty
LOW = FIFO above trigger level
HIGH = FIFO below trigger level or FIFO empty
INTA/B Pin
LOW = a byte in THR
HIGH = transmitter empty
LOW = FIFO above trigger level
HIGH = FIFO below trigger level or transmitter empty
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER
INTA/B Pin
FCR BIT-0 = 0
(FIFO DISABLED)
LOW = no data
HIGH = 1 byte
FCR BIT-0 = 1
(FIFO ENABLED)
LOW = FIFO below trigger level
HIGH = FIFO above trigger level
2.9 Crystal Oscillator or External Clock Input
The V2550 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. For programming details, see
““Section 2.10, Programmable Baud Rate Generator with Fractional Divisor” on page 10.”
FIGURE 4. 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 100 ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4). The programmable Baud
Rate Generator is capable of operating with a crystal oscillator frequency of up to 32 MHz at 2.5V. However,
with an external clock input on XTAL1 pin, it can extend its operation up to 64 MHz (16 Mbps serial data rate)
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