xr16l2750im Exar Corporation, xr16l2750im Datasheet - Page 6
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xr16l2750im
Manufacturer Part Number
xr16l2750im
Description
High-performance 2.25v - 5.5v Duart
Manufacturer
Exar Corporation
Datasheet
1.XR16L2750IM.pdf
(48 pages)
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xr
XR16L2750
2.25V TO 5.5V DUART WITH 64-BYTE FIFO
REV. 1.2.1
1.0 PRODUCT DESCRIPTION
The XR16L2750 (2750) integrates the functions of 2 enhanced 16C550 Universal Asynchronous Receiver and
Transmitter (UART). Each UART is independently controlled having its own set of device configuration
registers. The configuration registers set is 16550 UART compatible for control, status and data transfer.
Additionally, each UART channel has 64-bytes of transmit and receive FIFOs, automatic RTS/CTS hardware
flow control with hysteresis control, automatic Xon/Xoff and special character software flow control,
programmable transmit and receive FIFO trigger levels, FIFO level counters, infrared encoder and decoder
(IrDA ver 1.0), programmable baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 6.25
Mbps with 8X sampling clock rate or 3.125 Mbps in the 16X rate. The XR16L2750 is a 2.25 to 5.5V device with
5 volt tolerant inputs. The 2750 is fabricated with an advanced CMOS process.
Enhanced Features
The 2750 DUART provides a solution that supports 64 bytes of transmit and receive FIFO memory, instead of
128 bytes provided in the XR16C2850 and 16 bytes in the ST16C2550, or one byte in the ST16C2450. The
2750 is designed to work with low supply voltage and high performance data communication systems, that
require fast data processing time. Increased performance is realized in the 2750 by the larger transmit and
receive FIFOs, FIFO trigger level control, FIFO level counters and automatic flow control mechanism. This
allows the external processor to handle more networking tasks within a given time. For example, the
ST16C2550 with a 16 byte FIFO, unloads 16 bytes of receive data in 1.53 ms (This example uses a character
length of 11 bits, including start/stop bits at 115.2 Kbps). This means the external CPU will have to service the
receive FIFO at 1.53 ms intervals. However with the 64 byte FIFO in the 2750, the data buffer will not require
unloading/loading for 6.1 ms. This increases the service interval giving the external CPU additional time for
other applications and reducing the overall UART interrupt servicing time. In addition, the programmable FIFO
level trigger interrupt and automatic hardware/software flow control is uniquely provided for maximum data
throughput performance especially when operating in a multi-channel system. The combination of the above
greatly reduces the CPU’s bandwidth requirement, increases performance, and reduces power consumption.
The 2750 supports a half-duplex output direction control signaling pin, RTS# A/B, to enable and disable the
external RS-485 transceiver operation. It automatically switches the logic state of the output pin to the receive
state after the last stop-bit of the last character has been shifted out of the transmitter. After receiving, the logic
state of the output pin switches back to the transmit state when a data byte is loaded in the transmitter. The
auto RS-485 direction control pin is not activated after reset. To activate the direction control function, user has
to set FCTR Bit-3 to “1”. This pin is normally high for receive state, low for transmit state.
Data Rate
The 2750 is capable of operation up to 3.125 Mbps at 5V with 16X internal sampling clock rate, and 6.25 Mbps
at 5V with 8X sampling clock rate. The device can operate with an external 24 MHz crystal on pins XTAL1 and
XTAL2, or external clock source of up to 50 MHz on XTAL1 pin. With a typical crystal of 14.7456 MHz and
through a software option, the user can set the prescaler bit for data rates of up to 1.84 Mbps.
The rich feature set of the 2750 is available through the internal registers. Automatic hardware/software flow
control, selectable transmit and receive FIFO trigger levels, selectable TX and RX baud rates, infrared
encoder/decoder interface, modem interface controls, and a sleep mode are all standard features.
Following a power on reset or an external reset, the 2750 is software compatible with previous generation of
UARTs, 16C450, 16C550 and 16C650A as well as the 16C850.
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