RS-232 notes

RS232 notes

Alex tells me that 50' cables should be no problem, and that UCI used
to have rs-232 cables across campus: EG from ICS to the Administrative
building

Looks like an interesting "breakout box" based on *ix and two cables:

http://alexeyt.freeshell.org/code/serialdump.README

most basic RS-232 cable is 3 wires
The 3 minimum lines are: 1) ground 2) transmit and 3) receive
ground must be on the correct pin

straight through is "modem"
flipped is "null-modem"

with more than 3:
rts/cts are ready/clear to send, the original form of hardware handshake:
am i ok to send?  Yes, go ahead

...or...

dtr/dsr data terminal/set ready, normally on as soon as powered on,
comprises another form of hardware flow control, and a less standard one.
Some people felt that the DTR/DSR lines were wasted, so repurposed them
for flow control.

handshake means "flow control"

serial module sm16 is the cyclades 

normally pins 4 and 5 on an rj whatever, 8 pin serial connector will be
ground (the middle two), so you're grounded even if wired up in reverse.
If you touch a voltmeter to pins 4 and 5, the value should be near 0.
2.x is high enough to indicate a problem, maybe lower too

you can use rj* serial for ethernet, but only for very short distances.
You can use ethernet cables for serial, but:
1) only gigabit-capable ethernet cable works (because GigE requires
more lines?)
2) ethernet cables are harder to work with (harder to add connectors?)
3) ethernet cables are more expensive

Alex has two kinds of breakout boxes: one for 25 pin connectors (with
led's?) and one for rjmumble, without led's.  The latter makes it easy
to test using a voltmeter.

The lines with higher values (when connected to ground?) are likely
data lines, or does this just mean an active line?  I thought everything
might be 0, 5, -5, 12, or -12, rather than using magnitude to indicate
"data line"

db9 almost a std
5 gnd
2 xmt
3 rcv

cyclades str thru 

If you google up the pinouts for the equipment at both ends of the
connection, as well as whether each end thinks it's "a computer" or
"not a computer", then you can probably wire it up with that.  You may
also need to know what kind of flow control each end is expecting,
but this is often configurable.

Basically, if one end thinks it's a computer and the other doesn't,
then you wire up transfer to transfer, receive to receive, and ground
to ground, and maybe some flow control lines (RTS, CTS - or DTR, DSR)
if one or both ends won't do software flow control.

If both ends think they're computers, or both ends think they're not
computers, then you need to cross the transmit and receive lines - IE wire
up one machine's transmit to the other machine's receive, and vice versa.

Oh, and if you can get away with using a parallel or USB cable or
something else instead, you probably want to!  It'll probably yield both
faster communication as well as a faster hookup in terms of admin time.

From AIX-L:

here is the standard pin outs for a RJ-45 

Table 3-1  lists the pinouts and signals for the RJ-45 port. 
Table 3-1 RJ-45 Pinout for  networks {Ethernet}
 Pin     Description    
 1       Receive Data + (RxD+)  
 2       RxD-   
 3       Transmit Data + (TxD+)         
 6       TxD-   


RS-232C  serial connections (primarily for modem data transfer)
** Note:  direction of signals are relative to the respective each connector
        Legend:         <-- = incoming signal
                                --> = out-going signal
DB-9 female connector end
RJ-45 female connector end
 Pin#   Signal code                     Direction               Signal
 Description                      from                            Pin#
 Signal Code             Direction               Signal Description
 1                      CD
 <--                      Carrier Detect
 3                      DTR                      -->
 Data Terminal Ready
 2                      RxD
 <--                      Receive Data
 6                      TxD                      -->
 Transmit Data
 3                      TxD
 -->                      Transmit Data
 5                      RxD                      <--
 Receive Data
 4                      DTR                     -->
 Data Terminal Ready                                                     2
 CD                               <--                     Carrier
 Detect
 5                      GND                     ---
 System Ground                                                           4
 GND                      ---                     System Ground
 6                      DSR                     <--
 Data Set Ready                                                          1
 RI                               <--                     Ring
 Indicator
 7                      RTS
 -->                      Request to Send
 7                      CTS                      <--
 Clear to Send
 8                      CTS
 <--                      Clear to Send
 8                      RTS                      -->
 Request to Send
 9                      RI                              <--
 Ring Indicator

HTH
Jim Galloway
...
I forgot that there should be a jumper wire from pin# 1 to pin# 6 on
the DB-9 end as well

Great URL about RS232:

http://www.hw-server.com/rs232

A newer serial terminal concentrator than conserver:

http://www.jfc.org.uk/software/conc.html