Date   : Mon, 13 May 1996 16:35:04 BST
From   : Willble! ere Elk! Elk! Wolverene! <osu036@...>
Subject: correction

slight mistake forgot to show what connected

bbc                    pc
rts-----                       ------rts
           !                   !
cts----                        ------cts
txd ------------------------------------------ rxd
rxd ------------------------------------------txd
gnd -----------------------------------------gnd

On Mon, 13 May 1996 17:08:18 +0200 Mark de Weger wrote:

> From: Mark de Weger <deweger@...>
> Date: Mon, 13 May 1996 17:08:18 +0200
> Subject: Unidentified subject!
> To: bbc-micro@...
> 
> Hello everybody,
> 
> After this weekend's disaster with trying to connect my Beeb to a PC (couldn't
> get anything to work; still trying to work out what went wrong), I'm afraid I
> need a little more help. The problem is there's two "schools" of people with
> respect to connecting a Beeb's RS324 to a PC's RS232. My question is simple:
> who is right?
> 
> 1. The "keep it simple" school says just to crosswire Data-In and Data-Out,
>    to crosswire CTS and RTS and to connect the Beeb's ground to the PC's 
>    oV. The wiring would be like this:
> 
>    PC                      BBC
>    ==                      ==
>    0V            <--->     Gnd
>    Data In (RxD) <--->     Data Out (TD)
>    Data Out (TxD)<--->     Data In (RD)
>    CTS           <--->     RTS
>    RTS           <--->     CTS
> 
> 2. The "it's more complex" school says that the Beeb's RTS and CTS pins have
>    slightly different functions from the PC's. Instead, they say that the PC's
>    DTR pin has a similar function to the Beeb's RTS and the PC's DSR has
a similar
>    function to the Beeb's CTS. Thus the Beeb's CTS/RTS pins should instead be
>    connected as:
> 
>    PC        BBC
>    ==        ==
>    DSR <---> RTS
>    DTR <---> CTS
> 
>    Then there's a number of "extra's" people have given:
>    a. The Beeb's RTS pin should also be connected to the PC's DCD pin,
because the PC
>       looks on both DSR and DCD for a response.
>    b. The PC's RTS and CTS pins should be wired together.
>    c. The PC's DCD, DTR and CTS pins should be wired together.
> 
> The motivation for the first "school" is that's simply the way it works
(according to
> e.g. Gudmundur Thorsteinsson).
> 
> The motivation for the second "school" has been formulated by Paul Theobald
as follows:
> > The BBC's usage of the CTS and RTS are (arguably) different from the
RS232 usage, and
> > in fact more closely follow that of DSR/DTR.
> 
> Pete (pnt103@...) elaborates on that and also motivates
"extra's" 2a
> and 2b as follows:
> > The PC probably outputs a handshake on DTR and looks for responses
> > on DCD and DSR. These tell the device connected to the PC that the PC
is active (DTR)
> > and reply to say that the other device is present (DSR) and active (DCD).
Then RTS is
> > the PC's way of saying it wants to send (not just receive) and CTS is
the other
> > device's way of saying "go ahead"."
> 
> As Gudmundur pointed out to me, the "extra" 2c probably comes from wiring up an
> Archimedes to a Beeb, rather than a PC to a Beeb. (This is confirmed by the
> comp.acorn.misc FAQ; the Archimedes had a broken serial port controller
which made the
> extra wiring necessary.)
> 
> I'm sorry to bother you all again, but apparently things are not as simple
as it first
> appeared. Is there anyone who can tell me who's right? (And if it's school
2, which of
> the extra's a-c do I need.)
> 
> Thanxalot,
> Mark.
> 

               />      Christopher J. Thornley is OSU036@...
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