You will need to 'manage' the link at the application level if you don't use DTR/DSR and CD. AFAIK, getty looks for DSR/CD activity before giving you a login prompt. You can safely discard CD and wire that to DSR for a terminal.

Another side effect of not having DTR/DSR and CD is that if you power cycle the 'terminal' or otherwise break and make the link there is no hardware signalling to tell the NetBSD host to terminate and spawn another login. From a user experience it means that they never logged out - however the data on the screen is lost so they have to have some method of forcing a redraw or they'll enter data at a unknown cursor position.

In my implentations I found it preferable to live with XON/XOFF and DTR than RTS/CTS and no link status control. But that would depend on the speeds that you are driving, XON/XOFF is still acceptable up to 38k4 baud.v

--et

On Sat, 29 Jun 2002 00:39:39 -0400
"Andy Ball" <ball@cyberspace.org> wrote:

> 
> Hello!
> 
> I have an application where I need to connect a few serial
> terminals to a NetBSD host.  They'll be closer than 15m, so
> I shouldn't need any fancy RS-422 adaptors or anything.
> 
> My normal DTE-DTE 'null-modem' cable crosses over the data
> lines, RTS and CTS, and uses DTR at one end to drive both
> DSR and DCD at the other.  If there's at least one DB25
> connector, I connect the cable's screen to the frame ground
> at one end only.  It's a configuration that has worked well
> for me over the years.
> 
> Being the cheapskate that I am, I was wondering whether
> NetBSD normally uses the DTR, DSR or DCD pins to convey
> useful information between a host and a terminal.  If not,
> I was thinking that I could use 5 core cable instead of my
> usuall 7 core.  I'd loop back DTR to the DSR and DCD inputs
> at each end.
> 
> Off-the-shelf cables may work out cheaper, but that aside,
> is there any compelling reason why I shouldn't use the
> alternative wiring I've described?
> 
>    My normal DTE - DTE cable       Possible Alternative?
> 
>    9D                    25D
>    3 TXD -----\/----- TXD  2       TXD -----\/----- TXD
>    2 RXD <----/\----> RXD  3       RXD <----/\----> RXD
> 
>    7 RTS -----\/----- RTS  4       RTS -----\/----- RTS
>    8 CTS <----/\----> CTS  5       CTS <----/\----> CTS
> 
>    4 DTR -----\/----- DTR  20      DTR --,      ,-- DTR
>    6 DSR <-+--/\--+-> DSR  6       DSR <-+      +-> DSR
>    1 DCD <-'      `-> DCD  8       DCD <-'      `-> DCD
> 
>    5 SG  ------------ SG   7       SG  ------------ SG
> 
> The host in question is a PC, and the PC serial port may
> have some quirks <blatantly tenuous attempt to justify
> posting to port-i386 ;->
> 
> Regards,
>   - Andy Ball