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ST16C650A
2.90V TO 5.5V UART WITH 32-BYTE FIFO
REV. 5.0.0
1.0 PRODUCT DESCRIPTION
The ST16C650A (650A) is a low power UART that can operate from 2.90V to 5.5V power supplies. Its inputs
are 5V tolerant to facilitate interconnection to transceiver devices of RS-232, RS-422 or RS-485. The 650A is
software compatible to the industry standard 16C550 with some additional enhanced features.
The 650A provides serial asynchronous receive data synchronization, parallel-to-serial data conversion for the
transmitter section and serial-to-parallel data conversions for receiver section. These functions are necessary
for converting the serial data stream into parallel data that is required with digital data systems.
Synchronization for the serial data stream is accomplished by adding start and stop bits to the transmitted data
to form a data character (character orientated protocol). Data integrity is ensured by attaching a parity bit to the
data character. The parity bit is checked by the receiver for any transmission bit errors. The electronic circuitry
to provide all these functions is fairly complex especially when manufactured on a single integrated silicon
chip. The ST16C650A represents such an integration with greatly enhanced features. The 650A is fabricated
with an advanced CMOS process.
The 650A supports standard 8-bit Intel or PC bus interfaces through an input selection pin (SEL input pin). The
Intel bus uses the standard read and write signals for all bus transactions. The PC bus mode associates with
the PC ISA bus and follow the industry standard PC definitions for COM 1-4 serial port addresses. The 650A
includes on-board chip select decode logic and selection for the proper interrupt request. This eliminates the
need for an external logic array device.
The 650A has 32-bytes each of transmit and receive FIFOs, automatic RTS/CTS hardware flow control with
hysteresis, automatic Xon/Xoff and special character software flow control, selectable transmit and receive
FIFO trigger levels, wireless infrared encoder and decoder (IrDA ver. 1.0), programmable baud rate generator
with a prescaler of divide by 1 or 4, and data rates up to 3.125 Mbps with a 16X sampling clock rate.
The 650A is an upward solution that provides 32 bytes of transmit and receive FIFO memory, instead of 16
bytes provided in the 16C550, or none in the 16C450. The 650A is designed to work with high speed
communication devices, that require fast data processing time. Increased performance is realized in the 650A
by the larger transmit and receive FIFOs. This allows the external processor to handle more networking tasks
within a given time. For example, the standard ST16C550 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 32 byte
FIFO in the 650A, the data buffer will not require unloading/loading for 3.05 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 4 selectable levels of FIFO trigger interrupt and automatic hardware/software
flow control is uniquely provided for maximum data throughput performance especially when operating in a
multi-channel environment. The combination of the above greatly reduces the bandwidth requirement of the
external controlling CPU, increases performance, and reduces power consumption.
The rich feature set of the 650A is available through 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. In the PC
mode, two tri-state interrupt lines (IRQB and IRQC) and one selectable open source interrupt output (IRQA)
are available. The open source interrupt scheme allows multiple interrupts to be combined in a “wire-OR”
operation, thus reducing the number of interrupt lines in larger systems. Following a power on reset or an
external reset, the 650A is software compatible with previous generation of UARTs, 16C450, 16C550 and
ST16C650A.
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EXAR [ EXAR CORPORATION ]
