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1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 4 5
o o o o o o o o o o o o o o o o o o
25pin sub-d 9pin sub-d
o o o o o o o o o o o o o o o o
14 15 16 17 18 19 20 21 22 23 24 25 6 7 8 9
(pinout shown looking from soldering side)
pin pin sig signal name purpose
25p. 9p.
2 3 TXD Transmit Data outgoing data bits
3 2 RXD Receive Data incoming data bits
4 7 RTS Request to Send incoming handshake
5 8 CTS Clear to Send outgoing handshake (remote RTS)
6 6 DSR Data Set Ready (remote DTR)
8 1 CD Carrier Detect (remote carrier)
20 4 DTR Data Terminal Ready terminal ready status
7 5 GND System Ground signal ground
1 na FG Frame Ground signal shielding
note: FG should be connected only on one end of the cable!
wiring for NULLMODEM (DTE <=> DTE, ie 2 Computers):
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variation1: ("3-wire", no handshake)
RXD ----- TXD
TXD ----- RXD
GND ----- GND
FG ---( FG
this is not sufficient for most applications. if you really think this
is what you want to use, you probably know what you are doing.
variation2: ("5-wire", hardware handshake)
RXD ----- TXD
TXD ----- RXD
RTS ----- CTS
CTS ----- RTS
GND ----- GND
FG ---( FG
this works stable for simple applications, use this for prototyping and
alike :)
variation3: ("full", hardware handshake, status)
RXD ----- TXD
TXD ----- RXD
RTS ----- CTS
CTS ----- RTS
DTR ----- DSR
DSR ----- DTR
GND ----- GND
FG ---( FG
full "modem" status, except CD. not practical. (may not work for
programs that expect a modem, ie terminal-programs)
variation4: ("full local", hardware handshake, local status)
RXD ----- TXD
TXD ----- RXD
RTS ----- CTS
CTS ----- RTS
DTR ---+- DSR
+- CD
DSR -+
CD -+--- DTR
GND ----- GND
FG ---( FG
note: DSR + CD are bridged to fool programs to think that they are
online.
this is the suggested cable for endusers, it should work for any
program written for rs232 communications.
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