Re: TI-H: fargo fterm

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Re: TI-H: fargo fterm

On Fri, 15 Nov 1996, Mel Tsai wrote:


> Actually, the TI *does* send emulate RS232.  The TI doesn't have any
> "strange asynchronous protocol" and it doesn't send "raw bytes."
> RS232 is simply a format by which bytes are sent, i.e. baud rate, stop
> bits, parity, etc.  Fterm handles this for you.


I find this hard to believe, given that:


A. no TI calculator (not even the 92) has a reliable (i.e. crystal-based)
internal clock with which to time a baud clock.


B. The internal ROM routines on the 85 (and probably the 92, given that it
uses the same GRAPH-LINK cable and CBL as the 8x series calculators) use
one line for DATA and the other line for ACK (which is which depends on
the bit currently being sent). This is not RS232, this is a 2-line async
protocol, and it is used on the TI's for precisely the reason above -
without a reasonably stable clock, sending RS-232 isn't generally
possible.


What fterm does (which is what talk85 also does) is to send and recieve
individual bytes over the link port using the TI's standard routines. The
GRAPH-LINK has the smarts to translate bytes from TI's protocol to RS232
and vice versa.


> What the Graph-Link
> cable does is it converts the TTL voltages of the link port (+0V and
> +5V) to RS232 voltage levels (-15V and +15V).  There's probably some
> sort of MAX232 equivalent chip in the graph link cable. This
> conversion can't be done with just a few simple passive components.
> It requires a charge pump DC-DC converter, which is what the MAX232
> does (like in the connect 85).


No. You have accurately described the function of the long-discontinued 
LINK-85 product (aka "the black cable"), which TI used to sell. The
connect-85 hardware plans duplicate the functionality of LINK-85. However,
as a design it had many drawbacks - it did not use standard RS232, but
rather relied on the ability to manipulate serial port lines directly.
Thus, it was not usable on anything other than a PC-compatible.


The TI GRAPH-LINK is a rather more complex device which converts
TI's nonstandard protocol (well-described already) to standard RS232 with
proper voltage levels and all. It uses a custom PIC with other peripheral
circuitry to accomplish this. This is why it can be used with a Mac. More
importantly, this is why it can be used to connect a TI calculator to a
modem.


> As long as the TI-92 can keep the baud
> rates and bit format straight, it should be able to send/receive at
> any baud rate up to 14.4, but currently fterm isn't sophisticated
> enough to handle this.  In spite of this it may not be fast enough to
> handle 14.4 rates without a FIFO buffer, and you'll probably get a
> whole bunch of data overruns.


As I said already, the no TI calculator uses any specific baud rate. It is
the GRAPH-LINK hardware that converts between ti's protocol and 9600 baud,
8 bits, no parity RS232. The graphlink will not (to my knowledge) operate
at any other rate (higher or lower). 


BTW- fterm already gets buffer overruns at 9600. 


> Are you sure about this?  Some other people said that it does (I
> thought that someone was successfully using Lynx through their TI-92).


Quite sure. I've hooked up my 92 to my NetBSD machine as a serial
terminal. It does not support any VT control codes. To my knowledge, it
doesn't even support the CONTROL key, which is a real bummer.


You can run lynx, but it usually overruns the buffer on startup. Also, you
can't navigate (since lynx can't control cursor position on a dumb tty).
So lynx is next to useless. IRC works okay, though.


> Talk85 probably can't handle it.  Even if Talk85 used the ROM's send
> routines to get exact flow rates of 9600, there would be no way of
> sending certain characters and you couldn't handle full-duplex modes.
> There's also other flow rate and data format issues that Talk85 can't
> handle, so I doubt it will work.


Um, I've done it. It works. The GRAPH-LINK's circuitry handle all the
problems of duplex modes, etc. I'm sure it would not be hard to overrun
the buffer in talk85, but I've not tried hard enough to get to that point.


The only problem with Talk85 is that it doesn't send CR when you hit
enter - it sends LF. This means I could never get past the login screen.
However, sending and recieving characters with, say, C-kermit, works fine.
I can chat with the TI-85 without any problems.


With some judicious tinkering of some configuration files on my machine, I
could probably get it working. Not much point though - if you think 40x15
in fterm is painful, you've never used 21x4. :)


-Isaac


<pre>
--
Isaac Salpeter
the ticalc.org project
isaac@ticalc.org
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