Memorex CP8 TURBO UNIVERSAL REMOTE CONTROL Manual de usuario descargar pdf (Pagina 87)

100

The switching circuit in Fig. 8 steers

a single audio signal to a choice of

two

outputs. When

a positive

voltage

is ap-

plied to the anode of either

diode,

through

R2 or R3, its

internal resistance

goes from near infinity as an open

switch, to a low of a few ohms when

AUDIO

P -P

IN914

.27

10K

AUDIO

OUT

BIAS

INPUT

((f9

15V

Fig.

7 -This circuit uses a silicon

diode

to switch audio

from point "A"

to point

"B" by applying

a positive

voltage

to the bias circuit. The

switching

voltage can come

from a

mechanical

switch or

logic output.

closed. If both

switches are closed the

audio

will

be switched to

both outputs

A and B.

The diode-

switching circuit in

Fig. 9

uses a positive

voltage

switch input

"B"

the output circuit and a negative

voltage

switch input "A" to the out-

AUDIO

C1 01

IN914

`tel

IN914

10K

.27

Fig. 8 -The switching

circuit shown

here

steers

a single

audio signal

to a

choice

of two outputs.

When a positive

voltage is applied

to the anode of

either

diode, through

R2 or

R3. its

internal resistance goes

from

near

infinity as an open switch,

to a

low

a few ohms

when closed.

both switches

are closed

the audio

is fed to both outputs

A and B.

.21

.27

BIN

10K

1N914

10K

+ OR

15V

10K

OUT

A OR B

Fig. 9 -This

diode -controlled switch-

ing

circuit uses a positive voltage

switch

input "B" to the

output

circuit and a negative voltage to

switch

input "A" to the

output.

put.

All three of the diode

switching

circuits can

handle audio levels

up to 2-

volts

peak -to -peak, and

operate

with a

bias

voltage of 9 to 16.

Looks like

we have just about

filled

our cup for this

month. In closing,

wish

you all good

circuitry until the

next time

we meet.

FRIEDMAN ON

COMPUTERS

(Continued

on page 85)

reformed

at the

receiving

modem. It

also

maintains dynamic

tabulation

repeated characters

dynamic

meaning

continuous

updating.

In the compres-

sion process, any

unneeded data,

such

as a character

start bit,

for instance,

stripped off.

Under the

best of circumstances,

which

usually

means text

files, com-

pression

can provide up

to double the

throughput. In practical

terms, it means

that a 2400

-baud modem

can send in-

formation at the

rate of 4800 baud, al-

though

an 80 -85%

increase is more

typical. Also,

compression has little

effect

on highly

random data, such as

executable

files and

pre- compressed

data.

And assuming the

best of circum-

stances, if your computer

is feeding the

modem

at only 2400

baud, compres-

sion

or no compression, the

maximum

data -exchange

rate that is possible

2400 baud.

To get the

maximum possible

throughput,

it's necessary

to feed a

Class

5 modem as

fast as it can transmit

data.

That is done, as

shown in Fig. 1,

by providing

memory

within the

modem, and then

by outputting from

the computer

to the modem

at a much

higher baud rate, such as 9600

baud.

The computer

fills

the

modem's memo-

ry,

which

uses data -flow

control

(hand-

shaking) to

stop the flow of data from

the computer

when the memory is

full.

9600

BAUD

ORIG

NATE

COMPUTER

MODEM

RAM

2400 BAUD

DIAL

TELEPHONE

SYSTEM

MODEM

RAM

9600 BAUD

ANSWER

COMPUTER

EFFECTIVE

-DATA

BAUD

RATE

2400

-4800

BAUD

Fig. 1-In

order

for data compression

provide

an effective baud rate higher than

the actual baud rate of the modem, the data

flow from the computer

to the

modem

must be at least equal

to twice the modem's baud rate. By de

facto

convention, 9600

baud is becoming the "standard" computer output

rate when data compression

involved.

The modem then

transmits compressed

data. As the

memory empties,

the

handshake is released

so that the

com-

puter can again

output data to

the

modem's

memory.

Since the

computer

feeds data at an

even

faster rate

than the compressed

data can

exit the

modem, the modem

has no

wait

-state

unless the

receiving

modem

signals by

the error -correction

handshake that

it needs a

retransmis-

sion

of the last block

of data. Although

data

compression

requires that

the com-

puter

output into the

modem only

twice the

modern's baud

rate, by con-

vention

generally

output

from the

computer

to the modem

at rate of

9600

baud.

shown in Fig.

I, the receiving

answer modem can

also output

to the

computer at

9600 baud, although

does

not result

in throughput

beyond the

maximum effective

baud

rate,

which is

4800 bps. The

reason

receive

(an-

swer) at 9600 baud

is because

a con-

ventional serial port

must transmit

and

receive at

the same

rate, so if

we're

transmitting

at 9600

baud

must

re-

ceive

at 9600

baud.

course, data compression

tech-

niques can be applied

virtually any

modem. If, for example,

you

are using

9600 baud

on a dedicated

4 -wire tele-

phone circuit,

data compression

can

provide an effective

throughput

of up

19,200

baud.

Who

knows

how fast

next year's

effective

modem rate

will be? After

all,

it seems like

it was only yesterday

when

many

gurus claimed

that 1200'baud

was

the "ultimate

limit"

for the dial

-up tele-

phone system.

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