[futurebasic] Re: [FB] Hardware handshaking

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From: John H. Guillory <johng@...>
Date: Wed, 20 Feb 2002 14:07:55 -0600
On Tue, 19 Feb 2002 13:22:49 -0500, you wrote:

>I have found what I believe to be good pinouts for using hardware
>handshake. I am aware that both devices must be set to use the same
>protocol (I can choose between xon/xoff and DTR/DSR). 
Most modems have commands to enable Xon/Xoff, DTR/DSR, and CTS/RTS
handshaking.  The newer modems have a transparent xon/xoff mode that
is usually set by default.  The way this works is we assume your using
hardware handshaking, but if you transmit an xoff character to the
modem, we'll honour it and stop transmitting till you transmit an xon.
The only problem is in 8-bit downloads there's a chance the download
could send a x-off in the download packet of a file.  The download
either needs to be encoded in such a way to not allow an xoff
character being received or transparent needs to be turned off....

>Of course, I have no idea if my new cable that I have created is good,
>since I have yet to see any evidence of it working :)
Any idea on what HSKo and HSKi mean? I'm guessing something like High
Speed something out and in.... High Speed Control?  

>It goes like this (there is some voodoo):
>
>Mac Din-8      Serial Printer DB-25
>---------      --------------------
>1 (HSKo)       4 (RTS) AND 20 (DTR)  'handshake line
>2 (HSKi)       5 (CTS)               'I don't know if this is required
If pin1 goes to RTS and DTR, it'd seem that CTS and DSR would both go
to pin2....  Typically modems will assert RTS and DTR at the same
time, and perhaps the modem internally will basically have a similiar
setup internally....  Incidently, thanks for the mapping of the port,
would really love to know more about what HSKi and HSKo mean....

>My book for the printer says:
>RTS is a control signal from the printer to the host. RTS is in the ON
>condition (positive voltage) when the printer is powered on. When RTS is
>active, it indicates that the printer is ready to receive data.
  RTS stands for Request To Send, the modem normally will assert the
RTS line and the computer sees that the modem is ready to transmit
more data.  When it's ready to receive the data, it asserts the CTS
(Clear to Send) line.  The modem sees that the Clear to Send is set,
and it knows it can start sending data to the computer....  DTR (data
Terminal Ready) and DSR (Data Set Ready) work very much the same way,
except modern modems hang up when DTR is lowered and refuse to
communicate at all till DTR is raised.... Optionally, some modems can
be configured to perform the initialization string programmed for ATZ
upon a drop in DTR and return..... (perhaps useful if the modem is not
set to use hardware flow control by default, hanging up via DTR will
mean you have to re-enable hardware flow control on the modem before
you can start using it on the computer.... Actually, most term
programs will ignore Hardware flow control if the CTS is not high upon
entering the term program (acting like there's no modem there or no
hardware flow control), but if DTR is lowered and not raised, the
modem will pretty much appear to be dead till DTR is raised.... I used
to always leave my external modems set for Hardware Flow Control and
Transparent Xon/Xoff support, then in term programs that didn't
support hardware, I'd use Software and it'd work just fine.... Not as
good for high speed, but you could still see it working somewhat
better than no flow control....

>When DTR/DSR handshaking is selected, DTR is the ready control line from
>the printer to the host. When the DTR control signal from the printer is
>in the ON condition (positive voltage), the host may send data to the printer.
  DTR is the printer's Ready signal?  I'd imagine that the printer
would be a Data Set device, as most computers are Data Terminal
Devices..... I'd expect the DSR being the printer/modem's way of
saying its ready and the DTR being the computers sign that its
ready....