All trademarks mentioned in this document

are trademarks of their respective owners.

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

http://www.DigitalCoreDesign.com

http://www.dcd.pl

SYMBOL

datai(7:0)

address(2:0)

datao(7:0)

so

rts

dtr

out1

out2

cts

dsr

dcd

ri

wr

rd

cs

si

rst

clk

rclk

baudclk

baudout

intr

ddis

txrdy

rxrdy

D16550

baudclken

rclken

PINS DESCRIPTI O N

PIN

TYPE

DESCRIPTION

rst

input

Global reset

clk

input

Global clock

datai[7:0]

input

Parallel data input

addr[2:0]

input

Address bus

cs

input

Chip select input

wr

input

Write input

rd

input

Read input

rclk

input

Receiver clock

baudclk

input

Baud generator clock

si

input

Serial data input

cts

input

Clear to send input

dsr

input

Data set ready input

dcd

input

Data carrier detect input

ri

input

Ring indicator input

baudclken

input

Baud generator clock enable

rclken

input

Receiver clock enable

baudout

output

Baud generator output

datao[7:0]

output

Parallel data output

so

output

Serial data output

ddis

output

Driver disable output

txrdy

output

Transmitter ready output

rxrdy

output

Receiver ready output

rts

output

Request to send output

dtr

output

Data terminal ready output

out1

output

Output 1

out2

output

Output 2

intr

output

Interrupt request output

Note

: When enabled RCLK and BAUDCLK pins

frequency should be at least two times lower

BLOCK DIAGRAM

Data Bus Buffer

- The data Bus Buffer

accepts inputs from the system bus and

generates control signals for the other D16550

functional blocks. Address bus ADDR(2:0)

selects one of the register to be read

from/written into. Both RD and WE signals are

active low, and are qualified by CS; RD and

WE are ignored unless the D16550 has been

selected by holding CS low.

rclk

rclken

si

Receiver

Control

&

Shift Register

RCVR Buffer

&

RCVR FIFO

addr(2:0)

datai(7:0)

datao(7:0)

rd

wr

cs

ddis

txrdy

rxrdy

Data Bus

Buffer

Baud

Generator

clk

rst

Interrupt

Controller

rts

cts

dtr

dsr

dcd

ri

out1

out2

Modem

control

logic

so

Transmitter

Control

&

Shift Register

THR Buffer

&

THR FIFO

intr

baudclk

baudclken

baudout

Baud Generator

- The D16550 contains a

programmable 16 bit baud generator that

divides clock input by a divisor in the range

of the baud generator is 16× the baud rate.

The formula for the divisor is:

16

*

baudrate

frequency

divisor

=

Two 8-bit registers, called divisor latches DLL

and DLM, store the divisor in a 16-bit binary

format. These divisor latches must be loaded

during initialization of the D16550 in order to

ensure

desired

operation

of

the

baud

generator. When either of the divisor latches

is loaded, a 16-bit baud counter is also loaded

on the CLK rising edge following the write to