Re: Primitive File Transfer with Serial Port

Wolfgang.Schelongowski_at_gmx.de
Date: 06/28/05 

Date: 28 Jun 2005 17:50:47 +0200

scire@web.de writes:

>First of all: thanks to anybody for the answers, I learned a lot and
>spent some hours experimenting with the serial port and nullmodem
>cables.

>For the curious: how I half installed netbsd: thefloppy driver works
>from time to time, I booted the tiny rescue floppy, did fdisk,
>disklabel, mounted a swap partition (the laptop has less than 4 MB
>RAM), put a tiny kernel and some files (bin, sbin, etc, ...).

>I experimented with two cables, the first one so connected:

>1 4

??? Bad. DTR is now in the twilight of undefined (between +3V and -3V).

>2 3
>3 2

OK and necessary (TxD and RxD crossed).

>4 1

??? See above

>5 5

OK and necessary (GND == Signal ground).

>7 8
>8 7

OK and necessary for fullduplex (RTR[1] and CTS crossed).

>The second one so:

>1 1

OK, and IMO better.

>4 6
...
>6 4

DTR and DSR crossed. Hmmm... may do, but merely linking 4 and 6 on
each side and not connecting both sides may be better, and you
probably won't need clocal.

>9 9

DON'T. There is no ringing involved, so leave them alone.

>FOURTH QUESTION: wich of both cables is correct?

None, see above.

>I also discovered that the controler of the serial port of the old
>laptop does not have a fifo.

>FIFTH QUESTION: is it possible to have a software FIFO?

Apart from what jpd wrote: *Theoretically* it's possible, but you'd
need a fast local CPU which is idle all of the time. I.e. no disc I/O,
...

Final advice: If it doesn't work, slower the speed down.

[1] RTS is for halfduplex connections. For fullduplex the semantics
of that pin is no longer "I am Requesting To Send!" but "I am Ready To
Receive!". 

-- 
The first entry of Sin into the mind occurs when, out of cowardice or
conformity or vanity, the Real is replaced by a comforting lie.
  -- Integritas, Consonantia, Claritas