Re: Need Point-to-Point Patch for 14000 BAUD rate

[jaulick@access1.digex.net (JoAnn G. Aulick)]

dempson@actrix.gen.nz (David Empson) writes:

>stephen e buggie <buggie@indus.unm.edu> wrote:

>> I use POINT-TO-POINT modem software.  I've now got a Promodem 144e modem
>> by Prometheus.  Its an external modem connected to the modem serial port
>> of the Rom 3 IIgs.
>> 
>> The problem is that the two fastest speeds on Point-to-Point are:
>> 
>> 9600 BAUD and 19200 BAUD.
>> 
>> The modem goes 14400 baud at its fastest rate.

>You need to distinguish between two speeds here:

>- The speed at which the modem transfers data over the telephone line
>(the carrier speed, if you like).

>- The speed at which the modem and computer exchange data.

>These two are not necessarily the same for any modem faster than 2400
>bps (and even for some 2400 bps modems).

>If the modem supports error correction and/or data compression, then the
>computer-to-modem speed must be HIGHER than the modem's carrier speed.

>If the modem does not support error correction or data compression, and
>either the modem or computer has no support for handshaking, then the
>modem's carrier speed will match the speed at which the computer is
>connected to the modem.  (This applies to all 300 bps modems, all 1200
>bps modems that I know of, and most 2400 bps modems.)

>In the case of a 14k4 modem, you would normally be using error
>correction and data compression (either MNP-4 and MNP-5, or V.42 and
>V.42bis), so the computer should be set to talk to the modem at a speed
>higher than 14400 bps.  I have found that 19200 is sufficient.  (It is
>not optimal if you are sending or receiving uncompressed text data, for
>example, but it is good enough for most situations.)

>The main catch: handshaking is required between the computer and modem,
>so that the modem can tell the computer to stop sending data if it
>cannot keep up (depending on error recovery, how compressable the data
>is, etc.)  The best option is to use hardware handshaking.

>This raises the question: does Point-to-Point support hardware
>handshaking?  I don't know the answer to this.  If it obeys the IIgs
>Control Panel settings, then all you should need to do is enable DTR/DSR
>handshaking in the IIgs control panel, and ensure that your modem cable
>connects to the modem as follows:


>The pins on the IIgs connector are numbered as follows (looking at the
>back of the computer; swap these horizontally if you are looking at the
>pins on the cable):

>  8 7 6
> 5   4 3
>   2  1

>The cable pinout should be:

>IIgs    Modem (DB-25)
>  1      4             Handshake, computer to modem
>  2      5             Handshake, modem to computer
>  3      2             Data, computer to modem
>  4      7             Signal ground
>  5      3             Data, modem to computer
>  6     (no connection)
>  7      8             Carrier detect, modem to computer
>  8     (must be connected to IIgs pin 4 or modem pin 7)


>This is a standard "hardware handshake" cable for the IIgs (or Mac).
>The traditional modem cable connects the flow control signals (pins 1
>and 2) to the DSR and DTR pins on the modem, which are not used for
>handshaking.  If you are using an existing cable that was previously
>used with a slower modem, you will probably need to get it modified, or
>buy a new cable.

>In the meantime, your existing cable will only work reliably if you
>disable hardware handshake, error correction and data compression
>capabilities in the modem, and select 9600 bps on the computer.

>> BTW, I have a second identical ProModem 144e that does not work.  The CD
>> (carrier detect) lamp is always on.   I looked inside the modem case and
>> there are no obviously burned components.  Any suggestions????

>This might be a setting: the AT&C command is used with most modems to
>specify whether the Carrier Detect signal is to be used.  AT&C0 forces
>it to be permanently active, AT&C1 allows it to follow the real carrier
>detect state.

>If using AT&C1 does fix it, use AT&W to write the updated setting into
>the modem's nonvolatile memory.

>Ideally, you should do an AT&F to restore factory default settings, then
>go through the manual and identify which settings you wish to change,
>then write the settings using AT&W.

>A subsequent power-on or reset command (ATZ) will restore the saved
>settings.

>-- 
>David Empson
>dempson@actrix.gen.nz
>Snail mail: P.O. Box 27-103, Wellington, New Zealand