Mitsubishi Electric MUX-25TV - E1 User Manual download pdf (Page 67)

per motor

drivers,

a pulse

position modu-

lator,

and a two

-way UART

serial

com-

munications

channel interface

sound?

that's not

enough for you,

there are

enough pins

on the

package that

you

can

also use it for

an emergency

cheese

grater.

Obvious

uses for the

M50734 include

data recorders,

hydrophonic

garden

timers, cable TV

intelligent

taps, solar -

powered pump interfaces,

general robot-

ics,

weight

scales, cattlefeeder

setups,

stu-

dent trainers, hot

-tub pump

cyclers,

cotton -picker

tooth setter, numeric

machine

controls, etc.

It might

even be possible

to drop

this

dude

and an

adapter directly into

the

65CO2

socket

on an

Apple

IIc or IIe

and

run everything

else

out of a humongous

new

I/O

connector.

Stay tuned to this

col-

umn for more

details.

The

beauty

of being more

less

Apple

compatible is

that the full resources

of the

Apple

become available for

design, debug-

ging, and testing

what

you want

to do.

costly ROM

masks

or emulation

soft-

ware

needed,

and the design process

fast and fun

by using

standard assemblers,

debuggers,

printers,

disk drives,

etc.

Two

minor gotchas.

The

-pin,

70 -mil

shrink DIP

package is

oddball, so

sockets

may be very

difficult

to find. In

addition,

there

are not

enough pins

to go around,

they

used Motorola

style

multiplexing

on the data /low

address lines.

At worst,

this means

you

have

add a 74HC373

ad-

dress latch

to your final

circuit.

You'll

find

lots of information

on pro-

gramming

6502 -style

chips like

the

M50734

in my

two Micro

Cookbooks

SAMS

#2128 and 21829).

Tellyawhat.

Let's

have

us another

con-

test. A free

SAMS book

to the best 10

uses

for the M50734.

The

overall winner

gets

all expense

paid tinaja

quest for

two (FOB

Thatcher,

Arizona),

plus

some possible

cash type money

their entry is

good

enough to

become

a Modern Electronics

feature

or construction

article.

What

is a UART

There

are

two different

ways

of sending

data between

two points.

With parallel

data

communications,

all

bits

a data

word

are simultaneously

sent using

many lines

as there are

bits. Parallel data

communication is very

fast but need

lots of

wires.

On the other hand,

serial data

com-

munication

needs

only a single wire

to get

from

point A

to point B. All

bits are sent

down

the line one

at a time in

a specific

order.

Serial data communication

is much

slower

than parallel,

but it needs

only a

single

channel.

In general,

parallel

data

communication

used

inside

or near

computers,

while

serial data

links are used

between com-

puter systems,

particularly

over

long

distances.

Consider

the absurdity of

needing eight

separate telephones

at both

ends

to send 8 -bit

data

words.

There

are lots of times when you

want to

convert from

parallel data

to serial or

vice

versa.

For

instance, a lap

handicapped

keyboard would

best have its

data sent to

a computer in

serial form.

Some

com-

puters,

such as the Apple IIc,

output data

only

serial form.

You might like

to con-

vert

to parallel

outside

the computer

drive

a parallel

dot -matrix printer

or a

power controller full

of relays

or solid -

state

power switches.

Some

electronic

circuits do not have

microprocessor

them. Except

for the

simplest

computers, the main

micro-

processor in

a microcomputer

cannot

expected

to sit around

all day to generate

slow

serial code or wait

until new serial in-

put data

arrives. The

micro almost

always

has better

things to do.

Instead, there

are

many

special ICs

that convert data

from

serial

to parallel and

back again as needed.

They

are

cheap and easy

to get.

These

special

circuits are

called UARTs,

short

for

Universal Asynchronous

Re-

ceiver Transmitters.

The

"asynchronous"

the name means

that any amount of

time can go

by between successive trans-

missions

or receptions.

There

are two basic types of

UARTs.

hardwire

UART is used when there is no

microcomputer involved

at its end

of the

communication

channel. Two examples of

hardware

UARTs are the Intersil

IM6402

and IM6403. With hardwire

UARTs, the

data

formats are set by physical jumpers,

and the input

and output data appears

individual

lines.

A Peripheral

style

UART

is intended

for

use

with

controlling microprocessor. The

Rockwell

6551 is a typical

example.

With

a peripheral

UART, the data format

and

sometimes the data rate is

settable by soft-

ware. Input

and output

parallel data is

usually routed

directly to

the data bus on

the

controlling micro.

Figure

2 shows the

usual

format

of a

serial asynchronous

code.

This was

orig-

inally

called the Teletype

code.

Very

often

this

code

sent from

system to system by

using

-232C standard levels

and pin -

outs. Note

that a code and

standard

are

two totally

different things.

You

always

start

with

a start bit

that tells

the receiving

UART that

new

character

to arrive. Remember

that with

asyn-

chronous

communication, a random

amount of time can go

by between indi-

vidual

transmissions. The

actual code bits

then

sequential order. starting

with

the LSB,

least-

significant bit. After

the code bits

minimum

of one or two

stop

bits is sent,

followed by as many more

stop

bits

as you need to wait until

the next

transmission.

The

speed of transmission

is set

by the

baud rate. The

baud

rate

is defined

as how

fast the bits

come out of

the pipe.

Popular

START

BIT

DATA

BIT

(LSB)

DATA

BIT

DATA

BIT

DATA

BIT

DATA

BIT

DATA

BIT

DATA

BIT

DATA

BIT

(MSB)

STOP '

STOP

BIT

#1 I #2 I

Fig. 2.

The standard

8 -bit asynchronous

serial

code.

Say You Saw It

In Modern

Electronics

April

/986 /

MODERN

ELECTRONICS

/ 79

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