TTY - Teletype Terminal

[Dwayne]

Hello Fox,

Fox>>ok, im trying to figure out how to at least transmit the TTY tones... the only way i can think of doing it is using a crapload of If-Then statements. Kinda like this...


IF key="A" THEN
FREQOUT PORTB.1,40,1800
FREQOUT PORTB.1,40,1800
FREQOUT PORTB.1,40,1800
FREQOUT PORTB.1,40,1400
FREQOUT PORTB.1,40,1400
end if


then have the same for the rest of the characters. But i think it would be better to put whatever they keyboard data that comes by into memory, that way there is a buffer... but i have no idea how to do that.

Any other suggestions on how to do this?
<<

Ouch...Lets think about this a second ok? There are a couple of options.
It would be much better to represent your letters in a numeric or bionary form.
Letting one tone be 1's and the other be zeros'. but that poses a slight problem, because how are you going to represent letters that have 3 of the same tones, verse 2 of the same tones? One way to do this, it to have representations of one tone in one variable, and representation of the other tone in another variable.

Lets let one tone represent 1800hz and the other tone represent 2150hz ( I like thinking of it in "tones" instead of Mark,stop, space, and start bits.

Lets look at Morse code (which the idea is similiar to Baudot, except it uses 6 possible bits to print out the ASCII characters that Hams use.

T=_
M=_ _
O=_ _ _
9=_ _ _ _.

Notice the problem concerning the dashes or spaces? Using just a 1 and zero will not truely represent and differentiate between the characters.
T=0
M=00
O=000
9=00001
which all 3 equate to zero and if you attempt to use 1's to present dashes, you run into the same problem using 0's to represent the "dits".

One way to do such a thing, is the following: (letting 1 equate to dits)
Vs Var byte (keeps track of the dits...shorts)
Vl Var Byte (Keeps track of the dashes...long)

T:
Vs=%00000000
Vl= %00000001
$00,$01

0:
Vs=%00000000
Vl= %00000111
$00,$07

Now, lets take a "complicated" character... Like the period. It is of 6 characters in Morse, and baudot is in 5... but the same principal applies
.:
.-.-.-

Vs=%00101010
Vl =%00010101
$2A $15

Now, with this in mind, we can play a game of receive/shift!

Loop:
Vs=0;
Vl=0;
counter=0;
Loop2:
receive tone
if Tone length = correct (because you may have a 'pause')
{
(and a pause generates a tone!)
(on some machines! )
switch Tone

case tone=low
Vs[0]=1;
Vl[0]=0;
Vs<<1
Vl<<1


case tone=high

Vs[0]=0;
Vl[0]=1;
Vs<<1
Vl<<1

endswitch
counter =counter+1;
}endif (counter less than 6)
if counter<6 goto Loop2 (hey, get next tone!)
if counter =6 then Loop1 (error, too many tones)
}endif

Vs, and VL have your data , you could combine them into 1 word if you want, instead of 2 separate bytes.

Now you can do a couple of things from here... either a table lookup, or
a if/case statement.

switch VsVl
case VsVl=$0007
Print "O"
case VsVl=$2A15
Print "."

etc. etc. etc.

[Luciano]

See attachments.

Oscilloscope picture of the transition SPACE to MARK. The signal is generated with the sound card and the SW CallTTY v. 1.10.

Luciano

[Foxx373]

Damn Dwane, my head hurts now... I have no IDEA what the hell u said. I kinda get a little bit of how you did that whol thing, but im still a little fuzzy on the Vs Vl stuff. But i can see why you would wanna do it that way. honestly, i was trying to think of a way to do it like you did, but like i said, i am a total PicBASIC newbie.

[Dwayne]

Hello Foxx,

Foxx>>I kinda get a little bit of how you did that whol thing, but im still a little fuzzy on the Vs Vl stuff. But i can see why you would wanna do it that way. honestly, i was trying to think of a way to do it like you did, but like i said, i am a total PicBASIC newbie.<<

First things first...I wrote everything in Psuedo Code, because I am here at work. It is not EXACT code.

Lets look at a idea on how to receive the code.

Loop:

Receive tone
if too long of a pause, goto lookuptable
distinguish the tone value
store the tone in a variable
goto Loop

Lookuptable:
Take your variable, compare to a value
in the program or table and output

Goto Loop
*******************

Storing that "tone" in a variable is Vs and Vl

How are you going to distinguish the difference between the following:

__
__ __
__ __ __

and distingiush the following from above?
.
..
...

Using 1's and 0's can do it, but if they are used in just one 8 bit variable, you cannot distinguish the differences between the shorts and longs (marks and spaces). You have no place to start or stop through the entire 5 bits of data, because the whole 5 bits of data are exactly the same. to overcome this, you can use 2 variables that are 8 bit. (Vs and Vl) Vs will keep track of the shorts and Vl can keep track of the long. Both of them together will give the exact representation of the character coming across the signal.

For example the letters T,M,O represented by only one variable would look like this: (using 1 as short and 0 as long).
T = 00000000
M= 00000000
O= 00000000

On a lookup table, how are you going to represent 3 letters that are exactly alike?? they are all zeros! If you attempt to assign 1's to the long and 0 to the shorts, it looks like this:

T= 00000001
M= 00000011
O= 00000111

this is Good! but it poses another problem, how about characters that are the short sounds? Like E, I, and s?

E=00000000
I=00000000
S=0000000

Either side of the coin, using just one 8 bit variable is going to byte you in the 6 oclock. Now, lets introduce Vs and Vl.

T=__
Vs=%00000000 'there are no short tones
Vl= %00000001 'there is one high tone
$00,$01

0=__ __ __
Vs=%00000000 'there are no short tones
Vl= %00000111 'there are 3 long or high tones.

and if you go the opposite way (Lets take e and I)
e = .
Vs=%00000001
Vl=%00000000
$01,00

I= . .
Vs=%00000011
Vl =%00000000
$03,$00.

Thus "E" and "O" have a value that are NOT the same, and LIKE characters have a different value too.

Now you use a lookup table, or case statement, or IF statements.

if VSVL==$0300 then print out on LCD "I"
if VSVL==$0100 then print out on LCD "E"
if VSVL==$0003 then print out on LCD "M"
...
...

Sorry if this sounds confusing. I will try again.


Anyhow, first things first...

"Distinguishing the tones" Using PULSIN can give you how long your in the positive or negative stage of a wave. If you have this value, you can calculate the frequency of the wave, assign it a mark or space (short or long, or 1 and 0)

[Luciano]

Hi Foxx373,

I have collected (stolen) some material from the internet and
created a poster that will help you during this project.

(See attached file baudot.bmp , print=landscape).

Best regards,

Luciano


The source of the original material is:

async1.html, ©1998 All rights reserved
Tampa Bay Interactive, Inc.

[jctx79]

Hi Guys,
i was just curious the outcome of your project as i am considering a similar project and was curious if you were successful?
thanks