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
------------------------------------------------------
Article 2: 1995-01-11
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 that my solutions work with TI82 and a link82-program, I don't
know. I think it's harmless to try...
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.
--- BBBS/2 v3.141592653589793 Zebra
* Origin: Hangar, 951-3758236 / 3117053! (2:221/18)
