🚀 go-pugleaf

In article <twenty-1509971820250001@dialup-263.dublin.iol.ie>,
twenty@iol.ie-nojunkmail (Craig Lynch) wrote:

The basic problem is that the Mac serial port only has one output
signalling line, and ideally you need two output lines for high speed
modems - one for hardware handshaking (RTS), and one to signal that the Mac
is on and ready (DTR)

Appl'es recommended wiring for modem cables has the single output line
connected to both RTS and DTR. This means that if you're using hardware
handshaking and the Mac's buffer gets full and it asserts RTS to tell the
modem to stop sending for a moment, the Modem will also see the DTR line
change and will drop the connection *unless* you've told it to ignore the
DTR line.

However, some bits of software use software handshaking (XON/XOFF) rather
than hardware handshaking. These then use the output line to drop the ohone
connection, and so will neeed DTR recognition enabled.

I'd recommend that you nearly always disable DTR recognition with &D0 (or
whatever the equivalent is for your particular modem). Even software that
expects to be able to drop the connection with the DTR line will have
back-up ways to drop the line (by using the escape sequence +++ followed by
ATH0).

Paul Durrant

> I'm a bit confused about modem strings. I got this info from a BBS program
> called BulkRate:
> ____________________________________________________________
>  The bottom line is that in most instances, if you turn hardware
> handshaking on, you must set the modem to ignore the status of the DTR
> line. (Typically the correct command is &D0, though your modem may vary.) 
> Failure to do this will cause unwanted disconnects, especially when
> downloading or otherwise transferring a lot of data to your Mac.
> 
> Note also that this advice is not unique to BulkRate; it applies to all
> uses of high-speed modems with the Macintosh.
> ____________________________________________________________
> 
> But modem init strings for the mac always seem to have &d2 in them,
> meaning DTR disconnects. I have been using a string with &d2 in it for
> ages with no problem... apart from dropping the line once in a blue
> moon... and have changed it to &d0 now because someone said I should.
> Still no problems of course. I'm on a Performa 450. Can someone clarify
> this? If your modem will disconnect unless it's got &d0 in the string, why
> do all mac modem strings seem to have &d2 in them?
> cl