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Copyright 1999-2007 DCD – Digital Core Design. All Rights Reserved.

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D

0

Configurable UART with FIFO

ver 2.08

OVERVIEW

The D16550 is a soft Core of a Universal

Asynchronous Receiver/Transmitter (UART)

functionally identical to the TL16C550A. The

D16550 allows serial transmission in two

modes: UART mode and FIFO mode. In FIFO

mode internal FIFOs are activated allowing 16

bytes (plus 3 bits of error data per byte in the

RCVR FIFO) to be stored in both receive and

transmit directions. D16550 performs serial-to-

parallel

conversion

on

data

characters

received from a peripheral device or a

MODEM, and parallel-to-serial conversion on

data characters received from the CPU. The

CPU can read the complete status of the

UART at any time during the functional

operation.

Status

information

reported

includes the type and condition of the transfer

operations being performed by the UART, as

well as any error conditions (parity, overrun,

framing, or break interrupt). D16550 includes

a programmable baud rate generator that is

capable of dividing the timing reference clock

a 16 × clock for driving the internal transmitter

logic. Provisions are also included to use this

16 × clock to drive the receiver logic. The

D16550

has

complete

MODEM

control

capability, and a processor-interrupt system.

Interrupts can be programmed to the user's

requirements,

minimizing

the

computing

required to handle the communications link.

The separate BAUD CLK line allow to set an

exact transmission speed, while the UART

internal logic is clocked with the CPU

frequency.

Two DMA modes are supported: single

transfer and multi-transfer. These modes

allow UART to interface to higher performance

DMA units, which can interleave their

transfers between CPU cycles or execute

multiple byte transfers.

The configuration capability allows user to

enable or disable during Synthesis process

the Modem Control Logic and FIFO's Control

Logic,

change

the

FIFO

size.

So

in

applications with area limitation and where the

UART works only in 16450 mode, disabling

Modem Control and FIFO's allow to save

about 50% of logic resources.

The D16550 has universal microcontroller

interface, allows correct communication with

D16550 no matter how D16550 clock is

related to microcontroller clock. The core is

perfect for applications, where the UART Core

and microcontroller are clocked by the same

clock signal and are implemented inside the

same ASIC or FPGA chip, as well as for

standalone implementation, where several

UARTs are required to be implemented inside

a single chip, and driven by some off-chip

devices. Thanks to universal interface D16550

core implementation and verification are very

simply, by eliminating a number of clock trees

in complete system.