Texas Instruments TI-89 Tip List page 436

In line with this strategy, our first link cable (the black one (should be 'the gray one', Ed.)), utilized
relatively simple transistor circuitry and did not even use the RX and TX lines of the RS-232 port.
Instead, it used the RS-232 "control" lines (2 for inputs and 2 for outputs) to operate the data lines.
The reason we had to change away from this approach is that many Macintosh computers do not have
all the necessary control lines available on their serial port connections. To make a MAC compatible
connection we had to communicate through RX and TX and this required putting an eight-bit, crystal
controlled oscillator, PIC microcontroller in the cable. This microcontroller communicates with the PC
at a standard baud rate and converts each bit into the self clocking protocol to communicate to the
calculator. The power for the cable is derived from the PC and doesn't impose significant drain from
the calculator. Overall, this approach provides a reasonable cost link without any cost burden to the
calculator user who does not use a link to personal computers.
Due to the specialized components and also because some parts of the design are necessary to
ensure compliance with FCC radio frequency emission regulations, it is not practical for individual
users to build their own cables on a general basis. We hope this explanation helps you understand
why this is.
Extra spaces in front of each program line - why?
When you try to "Open" a group file on a Macintosh, you will receive an Information Window which
shows all lines of each program inside the group file. If you copy this and paste it into a new program,
you will see three extra spaces at the beginning of each line. To avoid these spaces, "Ungroup" the
group file instead of Opening it.
File size limitations - why can large files from my calculator not be opened?
Part of the difficulty here is tokenized size vs text size. The maximum 'text' size for editing (in the TI-82
and TI-83 software) is about 32k bytes. Tokenization reduces the size to much less (probably ~22k).
What this means is that keywords like 'Then', 'Disp', 'PlotsOn', etc. are 1 or 2 bytes tokenized vs 4 or
more in 'text'.
If you have a 23k program on your calculator in tokenized form (i.e. you created it on your calculator),
and then attempt to edit this using the Graph-Link, the editable text image probably exceeds the 32k
text edit limit. Basically, this large of a program is un-editable with Graph Link.
The workaround is not an easy one. The program has to be split into smaller segments (subprograms)
and each one edited separately.
Graph Link (DOS) interferes with my mouse or other serial card.
Graph Link works with the IBM standard communications protocols. Com1 and Com3 share an
interrupt request (IRQ), and Com2 and Com4 share an IRQ. Com1 and Com3 use IRQ 4 while Com2
and Com4 use IRQ 3.
Example: If you have a mouse on Com1 and have the mouse driver software loaded, you will have
trouble running Graph Link on Com3. Network cards can also cause such problems. You will need to
eliminate the IRQ conflict to have both devices working at the same time.
I cannot open a "protected" TI-82 program using my Mac Graph Link.
The older version of the Graph Link software for Macintosh would not allow users to read or update a
protected TI-82 program once it is saved. The new version of the Mac software has changed this
feature. Now, users can protect a program to be sent to the TI-82, but the user can still read and
update these programs from their computer.
The new software is now included in the Graph Link package.
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