More about the Practical Peripherals 2400SA modem:
Someone inquired about the Hayes compatibility of this modem. (Sorry, I'm
too lazy to go back and find the source article.) Chapter 9 of the modem
manual is "Compatibility." It lists the following exceptions to full
compatibility with a Hayes Smartmodem 2400:
"1. The PM2400SA operates with ASYNCHRONOUS RS-232C signals
only. Timing, Replies, Delays, and all other characteristics
should be 100% compatible with a Hayes Smartmodem 2400 in its
"2. There is no SYNCHRONOUS mode in the PM2400SA. The
Synchronous registers and command set functionality are FULLY
implemented, so from a software point of view, it looks like a
functional Synchronous mode."
"3. There is no `TR' LED on the front of the PM2400SA. This
LED is the DTR signal on the RS-232 connector and is monitored
and supported like the Hayes Smartmodem 2400."
"4. There are no Digital or Analog, Local or Remote Loopback
tests implemented in the PM2400SA. The PM2400SA does,
however, do a functional test of its Microprocessor, the
System ROM memory, its Non-volatile memory, and the Rockwell
modem chipset each time it is powered on."
"5. There is no `Dumb Mode Strap' in the PM2400SA. Therefore,
it will always understand commands sent it."
I used my PM2400SA for several hours over the weekend and continue to
be perfectly happy with it. I had one failed file transfer, which
turned out to be due to my wife picking up another extension on the
Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142-1214