Subject: Re: mac <-> pc serial cable for OFW serial console?
To: None <email@example.com>
From: Don Lee <firstname.lastname@example.org>
Date: 02/24/2003 15:41:26
If you're trying to use serial on MacPPC NetBSD, be aware that the
serial ports do not appear to work except as a console. Other
applications, such as PPP do not function.
If this has changed in the most recent updates, PLEASE correct
>> > So I've gotten a DIN8 serial cable connector. Now my question is
>>> this: do I need to use a null modem cable, or should the wiring
>>> between the Thinkpad and the powermac be straight through? The
>>> following, from http://www.netbsd.org/Ports/macppc/faq.html ,
>>> makes me think that the cable should be straight through:
>>You need a null-model.
>>> Your serial console settings should be 38400 bps, 8 bits, no parity,
>>> 1 stop bit, no flow control, and you can typically use a standard
>>> Mac "printer" cable to connect two Macs (even m68k-based Macs). See
>>> the NetBSD Serial Port Primer for additional help.
>>> I guess that printer cables would be straight through.
>>No. Mac-printer cables are null-modem cables.
> understanding the technology, part 194735e583g73.459a573.2658b5.tris
> Q: where do the RS-232/RS-422 come from? what was their original purpose?
> A: (once upon a time) they where to connect Data Communication Equipment (DCE, that is mostly _modems_ of any sort) to Data Terminal Equipment (DTE, that is computers, terminals, printers, etc.)
> the usual setup then looked like:
> replace DTE1 with your favorite flavour of computer
> replace RS* with yout favorite flavour of serial line standard (stds? soo many to choose of...)
> replace DCE with your favorite flavour of modem
> replace DTE2 with your favorite flavour of peripheral (or other computer)
> and this usual case uses so called 'straight' wired cables, due to the fact that DCE and DTE connector pinout is symmetrically same and of different gender (if case shape allows, you can connect a DCE 'dongle style' directly to a DTE without a cable in between) which also means that, speaking in terms of direction, a signal on a pin comes _out_ of one device but goes _in_ to the other device on the same pin
> why was it thought like this? back then when standards where such, computers used to be room-filling noisy and heating monsters that usually where banned to the cave, but user terminals had to be on the desks of the users, obviously many floors (and thus many meters of cable) away - far too distant for 'simple' interfaces and modems hat to be put in for coping with the distance
> (I beg pardon for omitting some details, for the sake of simplicity...)
> - - -
> now what are many geeks trying to do and some struggle because of lack of understanding (or memory about the story above)?
> when 2 specimen of DTEs are close enough to each other, e.g. a computer and a printer or two computers (one disguised as terminal, by mean of running a terminal emulation program) 'just a cable' is more elegant than the cable/modem/cable/modem/cable combo
> one is tempted to omit the modems, on short distances - herefrom the term 'null modem cable', a cable that avoids the use of modems
> a closer look to the new DTE---<RS*>---DTE situation reveals that the connectors of the two devices are IDENTICAL, in terms of gender and also, on a given pin, the signal comes _out_ by both devices (or _in_ on both, on other pins) - obviously it makes no sense to bring two _out_ resp. two _in_ signals together
> ==> the null modem cannot be a straight one, the appropriate pairs of conductors must be crosswired so to bring signals from _out_ pins to _in_ pins
> find of pinouts for various cables at http://www.hardwarebook.net/