[Kenwood] Straight and Null Modem serial cable

Mon, 14 Oct 2002 21:16:05 -0400 (EDT)

Hi,

Pins 2 and 3 are received data (RXD) and transmitted data (TXD); the 
specific pin definition depends on whether you are a serial port; Data Terminal
Equip (DTE) or a "modem"; Data Communication Equip (DCE).

A straight serial cable connects pin 2 on one end to pin 2 on the other

                                 pin 3 on one end to pin 3 on the other

This works when a serial port (DTE) is connected to a modem (DCE).

Null modem serial cable connects pin 2 on one end to pin 3 on the other

                                       on both ends.

This allows two serial ports (DTE) or two modems (DCE) to communicate. 

Hence Null modem cables are often simply called "swap" cables"

Sometimes manufacturers and their doc are wrong. Not infrequently one 
swaps pins 2 and 3 on one end (only) to "see if it will work".

Note that in virtually all cases, pin 7, ground, must be connected. 
Depending on what is connected to what and the degree to which the device 
driver or operating system is screwed up, various other pins (signals) may 
be connected or cross-connected in some fashion,

GL es 73,
Steve
KL7JT/1

On Tue, 15 Oct 2002, Edward B. Soriano, M.D. wrote:

> 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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