Re: NULL modem projects

[rubywand@swbell.net]

John Ruschmeyer writes ...

<< ....
   Maybe I should clarify. My assumption from all the "null modem" 
posts  is that there are a lot of people whose Apples have internal 
modems as opposed to serial cards. Further, many of these are of the 
300/1200 baud variety.
 
   In my limited experience, it seemed that such a modem consisted of 
some bus logic, a UART, and some modem circuitry. I was positing the 
question of whether anyone had taken an obsolete internal modem and 
converted it into a serial port. The advantage being that one *should* 
be able to get a higher transfer rate than is possible through the 
modem hardware.
 
 ....
 Any thoughts?
>> 

     The idea should work fine. At the least, you start with a nice 
circuit board which has power traces laid out and connections to Slot 
Data lines. A schematic of the modem would be a great help; but, since 
many of the IC's will be standard 'off-the-shelf' types, a builder 
could use IC data books to get pin-outs and function descriptions.

     Some data books will include serial interface application 
examples for UART and similar LSI IC's. It should not be too hard to 
diagram the parts of the circuit which should be retained.

     A manual and diagram for an existing Apple II serial interface 
will help set up the new interface so that it fits existing software. 
A check of a couple old interface card manuals indicates that Slot 2 
is where most wares expect to find the serial card. Evidently, $C0AE 
is the usual address for the Control register and Reading Status. 
$C0AF seems to be the usual address for Reading and Writing Data.
   
 
Rubywand