Hi Nate,
It does look like nStrobe can be used both for input and output.
However, using it for both at the same time is not trivial, and it seems
to me that that is what you wanted to do in your protocol.
I googled around a bit and was surprised to find how little data there
was on 8-bit parallel cables. I did find one page that describes one,
but with no mention of software to go with it.
http://www.teletechnics.co.nz/reference/cable/cable_data.html
I haven't looked at this cable too closely, so I don't know if it
verifies what I am about to say. If you connect data pins to data pins,
and strobe to ack, then I think you should be able to get your parallel
port to do buffered data transfer. If you do some ad-hoc wiring, you
will be able to transfer data, but you will have to generate all the
handshaking signals yourself, which will cost you a lot of time donig
ins and outs.
So my advice would be: Have a close look at how standard ECP/EPP transfers,
and wire your cable so that you can benefit from the automatic
handshaking functionality that your parallel port has built in. It will
make your transfers go much faster, and it will save you work.
Tell me what you think.
Blaise
Quoted from Nate Jenkins on Fri, Apr 18, 2003 at 09:59:23AM -0700.
> Blaise, et al.
>
> I appreciate your input. I have tried to not disregard the fact that some
> pins are input and others are output. Maybe my source is questionable...
>
> http://www.beyondlogic.org/spp/parallel.htm
>
>
> Hardware Properties
> .
> .<some copy snipped>
> .
> Pin No (D-Type 25) Pin No (Centronics) SPP Signal Direction In/out
> Register Hardware Inverted
> 1 1 nStrobe In/Out Control Yes
> 2 2 Data 0 Out Data
> 3 3 Data 1 Out Data
> 4 4 Data 2 Out Data
> 5 5 Data 3 Out Data
> 6 6 Data 4 Out Data
> 7 7 Data 5 Out Data
> 8 8 Data 6 Out Data
> 9 9 Data 7 Out Data
> 10 10 nAck In Status
> 11 11 Busy In Status Yes
> 12 12 Paper-Out / Paper-End In Status
> 13 13 Select In Status
> 14 14 nAuto-Linefeed In/Out Control Yes
> 15 32 nError / nFault In Status
> 16 31 nInitialize In/Out Control
> 17 36 nSelect-Printer / nSelect-In In/Out Control Yes
> 18 - 25 19-30 Ground Gnd
>
> Table 1. Pin Assignments of the D-Type 25 pin Parallel Port Connector.
>
>
> Specifically, on nStrobe, I read that it could be used for input or output.
> This is why I thought, it may be fine to connect. Is this not correct?
>
> I know I have tested with reading and writing to the data/status/control
> ports to see which bits I can use for outputting to the other PC using a
> LapLink cable. I think I double checked my pin assignments before I
> originally sent my inquiry to the list. Am I off? Where I am not certain
> is if I will damage hardware before attempting such a feat.
>
> Regarding an 8 bit cable, I have only seen the cable at http://www.lpt.com
> for 8 bit transfer. However, they will not even think about allowing their
> products to deviate from the world of M$. I have talked to them a few times
> about Linux support and they inferred that they cannot as if they were being
> watched right then by big brother... I think they have some extra circuitry
> in the cable to buffer and do some crossing over. That is why the cable is
> faster and very software dependent...
>
>
> Thank You,
>
> Nate Jenkins
>
> United Western Technologies
> Software Engineer
> http://www.uniwest.com
>
> nate@uniwest.com
> Ph: (509) 544-0720
> Fx: (509) 544-0868
>
>
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> ----- Original Message -----
> From: "Blaise Gassend" <blaise@gassend.com>
> To: "Nate Jenkins" <nate@uniwest.com>
> Cc: <linux-parport@torque.net>
> Sent: Thursday, April 17, 2003 4:11 PM
> Subject: Re: [PARPORT] custom cabling
>
>
> > > **Proposed Custom Cable Map**
> > > D7 - ~S7 , (09-11) , [data7-busy]
> > > D6 - S6 , (08-10) , [data6-nAck]
> > > D5 - S5 , (07-12) , [data5-paper]
> > > D4 - S4 , (06-13) , [data4-select]
> > > D3 - S3 , (05-15) , [data3-error]
> > > D2 - ~C3 , (04-17) , [data2-nSelPrntr]
> > > D1 - C2 , (03-16) , [data1-nInit]
> > > D0 - ~C1 , (02-14) , [data0-nAutoLF]
> > > ~C0 - ~C0 , (01-01) , [nStrobe-nStrobe]
> >
> > It seems to me like you are disregarding the fact that some pins are
> > inputs and others are outputs. For example, connecting nStrobe to
> > nStrobe won't work because they are both of the same type.
> >
> > I think there are some common designs for 8 bit parallel cables. They
> > connect the data lines to the data lines (on recent parallel ports the
> > data lines are usually bidirectional) and use the unidirectional signals
> > for handshaking. I don't have a link to a precise description of one of
> > these cables, but I expect that a little googling should help. I also
> > expect that the software for these cables is already available.
> >
> > Blaise
> >
>
>
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