XR16C2852 Datasheet, PDF (8/42 Pages) Exar Corporation – 3.3V AND 5V DUART WITH 128-BYTE FIFO

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3.3V AND 5V DUART WITH 128-BYTE FIFO
XR16C2852
REV. 2.0.0
2.8 INTA AND INTB OUPUTS
The INTA and INTB interrupt output changes accord-
ing to the operating mode and enahnced features set-
up. Table 3 and 4 summarize the operating behavior
for the transmitter and receiver. Also see Figures 18
through 23.
TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER
Auto RS485
Mode
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1
(FIFO ENABLED)
INTA/B Pin
NO
0 = a byte in THR
0 = FIFO above trigger level
1 = THR empty
1 = FIFO below trigger level or FIFO empty
INTA/B Pin
YES
0 = a byte in THR
0 = FIFO above trigger level
1 = transmitter empty 1 = FIFO below trigger level or transmitter empty
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1
(FIFO ENABLED)
INTA/B Pin 0 = no data
1 = 1 byte
0 = FIFO below trigger level
1 = FIFO above trigger level
2.9 CRYSTAL OSCILLATOR OR EXT. CLOCK INPUT
The 2852 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 “Programmable Baud Rate Generator.”
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS
XTAL1
XTAL2
R2
500 ΚΩ − 1 ΜΩ
R1
0-120 Ω
(Optional)
C1
22-47 pF
1.8432 MHz
Y1
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 20-80 ohms and 100ppm frequency tol-
erance) connected externally between the XTAL1 and
XTAL2 pins (see Figure 4). 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.
2.10 PROGRAMMABLE BAUD RATE GENERATOR
A single Baud Rate Generator (BRG) is provided for
the transmitter and receiver, allowing independent
TX/RX channel control. The programmable Baud
Rate Generator is capable of operating with a crystal
frequency of up to 24 MHz. However, with an external
clock input on XTAL1 pin and a 2K ohms pull-up re-
sistor on XTAL2 pin (as shown in Figure 5) it can ex-
tend its operation up to 50 MHz (3.125 Mbps serial
data rate) at room temperature and 5.0V.
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