BBS: Metropoli
#1944  100:Email  10-Jan-95  15:31  (-/-)  (P)
erikst@Minsk.DoCS.UU.SE => calc-ti@ds0.internic.net
Subj: Calc-TI - TI85 Cable!

Hello!

I have just made my home made link cable (TI85 <-> PC) work.

Texas doesn't use a standard serial interface, instead they use two
input/output lines with TTL-levels. The problem is first to convert
RS232C-levels (-15 and +15 volt) to TTL-levels (0 and 5 volt). Then you
must invert some of the signals and merge the computer's four lines
to just two input/output-lines.

I used one circuit (MAXIM MAX232CPE, the prize is about $6 in Sweden) to
make the signal conversion, one 74HC04 ($0.50 perhaps) to invert some
signals, five condensators to make the MAX232CPC-circuit work and
two 6.8k resistors to merge the two output-lines and the two input-lines
from the computer to just two input/output-lines. Unfortunally my
solution requires +5 volt external power supply, though I think that you 
can take that from the game-port.

I believe that it's possible to make a cheaper solution with just one
circuit, but it requires +5 volt too. Therefore I suggest that we use the
printer-port instead! Then the only hardware you need is two resistors!
Of course the software on the PC must be rewritten, but that's VERY easy to
do if we only have the source. I believe that there already exists some
free link software for the PC, and if the person who wrote that
software reads this and thinks that my idea is good, please contact me.


Erik Starback (with dots over the second a)

Email: erikst@student.docs.uu.se

BBS: Metropoli
#2223  100:Email  13-Jan-95  15:02  (-/-)  (P)
erikst@Minsk.DoCS.UU.SE => calc-ti@ds0.internic.net
Subj: Calc-TI - Link-Cable wiring diagram


Here are two wiring diagrams for a TI85-Cable. Of course
you make them at your own risk, but both works fine with my TI85
(with ROM 9.0) and link85x.exe. I think my TI85 is a CBL-calc... (it
is written "CBL"" at the sticker with the serial number) but I really
don't know what that means. I just bought my calculator a couple of
weeks ago. May anyone explain that for me?

I have no idea if any of these solutions works with older calculators,
but I think it's harmless to try.

The difference between the two
solutions is that version 1 uses a special circuit to convert
the signal-levels, and version 2 uses a more primitive signal-level conversion.

It's possible it works with TI82 and a link82-program. I don't know, but I
think it will work.

I hope you can understand my lousy ASCII-drawing.

Version 1:

R1-2: 6k
IC1: 74HC04
IC2: Maxim, MAX232
C1: 4.7uF/6.3V
C2: 4.7uF/16V
C3: 10uF/16V
C4: 10uF/6.3V
C5: 10uF/6.3V


TI85                                                    PC Serial Port
                                           IC2             (25 pin)
                          IC1           +--------+
  White                 |\              | TTL    |            DSR
<>-----------+----------| >O------------| to     |--------------->
             |        1 |/   2       10 | RS232C | 7           6
             |                          +--------+
           +-+-+
           | R |
           | 1 |
           +-+-+                           IC2
             |          IC1             +--------+
             |            /|            | RS232C |            DTR
             +----------O< |------------| to     |---------------<
                      4   \| 3        9 | TTL    | 8          20
                                        +--------+


                                           IC2
                          IC1           +--------+
  Red                   |\              | TTL    |            CTS
<>-----------+----------| >O------------| to     |--------------->
             |       13 |/   12      11 | RS232C | 14          5
             |                          +--------+
           +-+-+
           | R |
           | 2 |
           +-+-+                           IC2
             |          IC1             +--------+
             |            /|            | RS232C |            RTS
             +----------O< |------------| to     |---------------<
                     10   \| 11      12 | TTL    | 13          4
                                        +--------+


  GND                                                         GND
<>---------------------------------------------------------------<>
                                                               7

Besides every connection mentioned in the big diagram you must make some
more connections on the IC2 to make it work.  See below (all pin-numbers at
IC2):

1  |      4  |      2  |    GND |    +5V |        +5 volt to 16
   |+        |+        |+       |+       |+       GND to 15
  ===       ===       ===      ===      ===
C1 |      C2 |      C3 |     C4 |     C5 |
   |         |         |        |        |
 3 |       5 |     +5V |      6 |    GND |

and of course you must give IC1 some power (now it's IC1!):  +5v to 14
                                                             GND to 7

White at the TI85 is the middle connector at the 2.5mm phono-plug and Red
is the tip-connector of the plug. Guess which one that is GND? :-)
Hmm, I'm not sure it's a standard 2.5mm plug. I used the TI85<->T85-cable.

R1 and R2 isn't critical. I think you can use some resistors between
2 and 20k, but I haven't tried it...

I think you can use LS, HCT or some other sort of 7404, but... you know
what I'm going to say... :-)

End of version 1
--------------------------------------------------------------------
Version 2

This version uses a simple RS232C to TTL conversion which consists of
4 silicon diodes. If any of the diodes breaks AND the 74HC08 breaks
because of that (that's certainly not sure) then it's POSSIBLE that the
TI85 falls to pieces... I think it's rather safe, but I take no
responsibility. I use this version myself.

When it comes to TTL to RS232C conversion it's even more simple, it
doesn't make any conversion at all! Most RS232-interfaces accept 0V as
-15V and +5V as +15V. Both my old Atari ST and my PC do that. Voila! A
very cheap solution.

R3-6: 6k
IC3: 74HC32
D1-D4: Just four ordinary silicon diodes... They should tolerate about 25V
       reverse voltage. Almost every diode do that.


TI85                                                             PC Serial Port
                                                                    (25 pin)
                          IC3
  White                 |\                                               DSR
<>-----------+----------| >------------------------------------------------->
             |        1 |/  3                                             6
             |
           +-+-+                       +5V _
           | R |                           |
           | 3 |                         __|__
           +-+-+                      D1  /^\
             |          IC3              +-+-+
             |            /|               |          +--------+         DTR
             +-----------< |---------------+----------|   R4   |------------<
                       6  \| 4           __|__        +--------+          20
                                      D2  /^\
                                         +-+-+
                                           |
                                       GND -

                          IC3
  Red                   |\                                               CTS
<>-----------+----------| >------------------------------------------------->
             |       13 |/  11                                            5
             |
           +-+-+                       +5V _
           | R |                           |
           | 5 |                         __|__
           +-+-+                      D3  /^\
             |          IC3              +-+-+
             |            /|               |          +--------+         RTS
             +-----------< |---------------+----------|   R6   |------------<
                       8  \| 10          __|__        +--------+          4
                                      D4  /^\
                                         +-+-+
                                           |
                                       GND -

  GND                                                                    GND
<>--------------------------------------------------------------------------<>
                                                                          7

IC3 must have some more connections to work. Connect: 1 to 2, 4 to 5,
9 to 10 and 12 to 13. And last but not least: 7 to GND and 14 to +5V.

You can exchange IC3 to a 74HC08 if you want (not tested...). As you
see, I'm just using the gates as buffers.

Red and White is - of course - exactly as in version 1.

End version 2
---------------------------------------------------

I still think that my idea to use the printer port and rewrite the
link software is good. But if you think this is better, it's OK with me...

Please mail me if you get any of my solutions working.

Regards

Erik Starback

Email: erikst@student.docs.uu.se

BBS: Metropoli
#2679  100:Email  13-Jan-95  22:45  (-/-)  (P)
erikst@Minsk.DoCS.UU.SE => calc-ti@ds0.internic.net
Subj: Calc-TI - answers about my "pirate-cable"


Some answers about my home made TI85<->PC-Cable:

Stephane 'Peekaboo' Jantzen wrote:

> Is the simpliest version really dangerous for TI ?

I can't be sure how dangerous it is. Earlier I said:
"If any of the diodes breaks AND the 74HC08 breaks
because of that (that's certainly not sure) then it's POSSIBLE that the
TI85 falls to pieces... I think it's rather safe, but I take no
responsibility. I use this version myself."
That's not the whole truth. If the 74HC08 breaks, it must do it in a very
unlucky way to make the disaster possible.

It's of course much safer if do some measuring before you connect the
TI85:

Before you start the link85x.exe program: The point between D1 and D2
(D3 and D4) should be about -0.7V. Pin 1 and 13 at IC3 should be about
0.0V.
After you have started the program: The point between D1 and D2
(D3 and D4) should be about +5.7V. Pin 1 and 13 at IC3 should be about
5.0V.

As I have already said: I think it's better to use the printer-port.
Then it's totally (hmm...) safe. Please, link-software-experts, contact
me!
---------------------------
Michael Wrighton wrote:

> Have you tried this with the Windows link software?

No, the only link program I have is link85x.exe...

I would be glad to test my cable with every existing link-program.
Maybe someone can mail (uudecode and compressed of course) them to me.
I don't think Texas has to be too upset about this. I will erase them
after the experiment.
--------------------------------
And now something about law and order...

I think that the link85x.exe program is free. If it's not, please mail
me a note. Link85x.exe is however a little bit primitive, and it would
be nice with a good free link-program.

It seems to me that some think it's illegal to build or help other to
build "pirate-cable". I can't see why. As long as you don't copy Texas
construction, or use their commercial software.


Erik Starback
Email: erikst@student.docs.uu.se
