Re: TI-H: connect-85 problems
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Re: TI-H: connect-85 problems
> Has anyone actuly built a connect-85, that works?
I tried once, but it was more complicated than useful. That and I found
the schematic for the "$4 Link" to be much simpler and just as functional.
> I have built the connect-85 and have been unable to use it successfully
> with the connect-85 software. I have also tried useing almost all of the
> other software programs listed on ti-calc.org, all of which were
> unsuccessful. I have tested the hardware using a break-out box and have
> foud it to work fine. I had to modify the harware to prevent the
> calculator from being slowed down, by tieing the the inverter (74ls04)
> outputs to gound with a 1K resistor and beef up the 6K to 120K. I have
The calc slowing down usually indicates that the serial port has not been
initialized by the software. This phenomenon occurs on the "$4 Link" as
well. It will usually disappear within about 3 seconds of initializing the
serial port properly.
> also tested the serial port using Cross Talk (XTalk) and to computers,
> and have found no problems using either comm1 or comm2. I tested the
> port on the calculator by sending a program to another calculator. This
> gives me reason to believe that the software is not working properly.
> can anybody offer a suggestion as to what might solve my problems? I am
Test all the parts. On the MAX232, try feeding +/- 12v on the RxIN pins
and check that TTL (0/5v) comes out at RxOUT. The put TTL signals (again,
0/5v) on the TxIN pins and check for +/- 12v at TxOUT. On the 7404, make
sure that it does actually invert whatever you feed into it. Make sure the
capacitors are all functioning and connected in the correct direction. Try
putting the 6k resistors back in. If all else fails, build the $4 Link. I
can almost guarantee it'll work, and you'll need no more than $3 in
additional parts. Depending on where you get parts, they could total as
little as $0.50. Then again, if you cannabilize them from some other
appliance, it won't cost anything.
> confused as to why the link does not use pins 2$3 of the serial port.
> Can anybody offer an explanation for this? I have also tried the $5
The reason lies in the functioning of the TI link port. You've surely
noticed how easy it is to interface TTL logic like expanders, I2C chips,
PICs, AVRs, and the like to the link port. This is because the link port
is really just a two-bit I/O port from the processor. It does not use any
variation of the RS-232C standard.
On the PC serial port, there is no easy way to check the status (high/low)
of the Tx and Rx pins. The work-around is to use the handshaking lines as
data lines instead. There is a problem here, however, because the
handshaking lines are not bidirectonal--but the TI link port is. So the
zener diodes (on the "$4 Link"--the 7404 on the Connect-85 is for the same
purpose) are used to prevent the output of the calculator and the output
of the serial port from shorting each other. They serve as a one-way
street for the electrons.
So basically the data travels over 4 handshaking lines rather than the two
data (TX/RX) lines. This makes the hardware (as well as the software)
easier to design.
As for the "$4 Link" connection on pin 3, a voltage reference was needed
to get the rest of the circuit working. While the cable is in operation,
pin 3 just stays set to the same voltage value.
Wow.. did that all make sense?
--
Greg Hill
greg-hill@bigfoot.com
www.comports.com/link
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