XR16C2852_05 Datasheet, PDF (9/51 Pages) Exar Corporation – 2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS

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REV. 2.1.1
XR16C2852
2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
TABLE 2: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE
PINS
FCR BIT-0=0
(FIFO DISABLED)
FCR BIT-0=1 (FIFO ENABLED)
FCR BIT-3 = 0
(DMA MODE DISABLED)
FCR BIT-3 = 1
(DMA MODE ENABLED)
RXRDY# A/B
LOW = 1 byte
HIGH = no data
LOW = at least 1 byte in FIFO
HIGH = FIFO empty
HIGH to LOW transition when FIFO reaches the
trigger level, or timeout occurs.
LOW to HIGH transition when FIFO empties.
TXRDY# A/B LOW = THR empty LOW = FIFO empty
LOW = FIFO has at least 1 empty location
HIGH = byte in THR HIGH = at least 1 byte in FIFO HIGH = FIFO is full
2.8 INTA and INTB Ouputs
The INTA and INTB interrupt output changes according to the operating mode and enahnced features setup.
Table 3 and 4 summarize the operating behavior for the transmitter and receiver. Also see Figures 20
through 25.
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
LOW = a byte in THR
LOW = FIFO above trigger level
HIGH = THR empty
HIGH = FIFO below trigger level or FIFO empty
INTA/B Pin
YES
LOW = a byte in THR
LOW = FIFO above trigger level
HIGH = transmitter empty HIGH = FIFO below trigger level or transmitter empty
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0
(FIFO DISABLED)
INTA/B Pin 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 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.”
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