[Kenwood] Straight and Null Modem serial cable

[DHauer]

Ok -Here's the difference.  But first, a simple explaination on terms
beforehand...

A PC, dumb terminal or printer is classified in the interface world as a
"DTE" = Data Terminal Equipment.

A modem, multiplexer, or DSU (Digital Sending Unit), etc. is classified as a
"DCE" = Data Communications Equipment

The above terms apply primarily to the old, traditional RS232-based
interface whereby: Pin #2 is TX, Pin #3 is RX, and Pin #7 is ground on a
DB25 connector (I believe for a DTE, if memory serves me correct).
Then...for a DCE; Pin#2 is RX, Pin #3 is TX and Pin #7 is ground.

You would normally use a "straight-thru" cable to connect a DTE directly to
a DCE.

You MUST use a "null-modem" cable to connect a DTE to another DTE.

Why?  Because it ensures that the TX Pin from the one DTE device gets
connected to the RX Pin of the other DTE device (and vice/versa), plus, it
ensures that standard control signals on other Pins get appropriately
connected - such as RTS (Request to Send) and CTS (Clear to Send), etc..

Please bear in mind, RS232 cabling usually supports MORE than just TX, RX
and Ground.  For example, the DCE device will provide control signals such
at RTS/CTS (for hardware data flow-control), plus DSR (Data Set Ready) and
possibly a clocking signal for certain applications, etc. - these signals
will of course be on other Pins.

Correspondingly, the DTE device may also use RTS/CTS signals for hardware
flow-control and will often times supply a DTR (Data Terminal Ready) signal
and may be able to receive (if it's configured as "slave") a clocking signal
(for certain applications) - these signals will also be on other Pins.

Sometimes, manufacturers use different connector types (such as DB9) and,
non-standard pinouts for supplying/receiving signals.  Sometimes they "don't
care" about certains signals ... or, they do.  Carefully reference the
equipment interface specifications in that case.

Hope that this helps.

- 73  Dieter, WB3JWU

----- Original Message -----
From: "Edward B. Soriano, M.D." <soriano.md@pacific.net.ph>
To: <yaesu@mailman.qth.net>; <icom@mailman.qth.net>;
<kenwood@mailman.qth.net>
Sent: Tuesday, October 15, 2002 5:14 AM
Subject: [Kenwood] Straight and Null Modem serial cable


Sorry for the ignorance. Can someone tell me the difference between a
"straight serial cable" and a "null modem" type of serial cable.

Been trying to connect my FT847 to my notebook with no avail. No problem
with my FT 920. The manual says one must use the null modem type. Not sure
if I got the right one.

Software is LOGIC 5.2

Thanks!

Edward B. Soriano, M.D.
4F1OZ also W3DOC


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