Re: TI-H: connect-85 problems
[Prev][Next][Index][Thread]
Re: TI-H: connect-85 problems
I have tested all the functions of the 7404 and max232 and they check
out fine. The voltages comming from the max232 are +/-8v which should
not make a difference since the RS-232 inputs are +/-3v to +/-25v. I
checked the polarity on the caps with both the manufactuers recomended
setup and the connect-85 schematic which match perfectly.
The main question I have now is how do the programs interface with the
flow control? If it is possible can you send me some sorce code to look
at?
When I get some zeners I am going to try and build the $4 serial link.
Do you have any idea as to why the parallel link that built did not work
ethier?
-mj
Greg Hill wrote:
>
> > 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
Follow-Ups:
References: