XR16M781 Datasheet, PDF (5/52 Pages) Exar Corporation – 1.62V TO 3.63V UART WITH 64-BYTE FIFO AND VLIO INTERFACE

XR16M781
REV. 1.0.1
1.62V TO 3.63V UART WITH 64-BYTE FIFO AND VLIO INTERFACE
1.0 PRODUCT DESCRIPTION
The XR16M781 (M781) is a high performance single-channel UART with a VLIO bus interface. It has its set of
device configuration registers. The configuration registers set is 16550 UART compatible for control, status
and data transfer. Additionally, the M781 channel has 64 bytes of transmit and receive FIFOs, Automatic RTS/
CTS Hardware Flow Control, Automatic Xon/Xoff and Special Character Software Flow Control, infrared
encoder and decoder (IrDA ver 1.0 and 1.1), programmable fractional baud rate generator with a prescaler of
divide by 1 or 4, and data rate up to 20 Mbps. The XR16M781 can operate from 1.62 to 3.63 volts. The M781
is fabricated with an advanced CMOS process.
Larger FIFO
The M781 provides a solution that supports 64 bytes of transmit and receive FIFO memory, instead of 16 bytes
in the XR16L580. The M781 is designed to work with high performance data communication systems, that
requires fast data processing time. Increased performance is realized in the M781 by the larger transmit and
receive FIFOs, FIFO trigger level control and automatic flow control mechanism. This allows the external
processor to handle more networking tasks within a given time. For example, the XR16L580 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 115.2Kbps). 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 M781, 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.
Data Rate
The M781 is capable of operation up to 20 Mbps at 3.3V with 4X internal sampling clock rate. The device can
operate at 3.3V with a 24 MHz crystal on pins XTAL1 and XTAL2, or external clock source of 80 MHz on XTAL1
pin. With a typical crystal of 14.7456 MHz and through a software option, the user can set the prescaler bit and
sampling rate for data rates of up to 3.68 Mbps.
Enhanced Features
The rich feature set of the M781 is available through the internal registers. Automatic hardware/software flow
control, programmable transmit and receive FIFO trigger levels, selectable baud rates, infrared encoder/
decoder, modem interface controls, and a sleep mode are all standard features. MCR bit-5 provides a facility
for turning off (Xon) software flow control with any incoming (RX) character. The M781 includes new features
such as 9-bit (Multidrop) mode, auto RS-485 half-duplex direction control, different baud rate for TX and RX,
fast IR mode and fractional baud rate generator.
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