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RS-232 Cabling for -LOOP Option in CT Version 9
There are two types of RS-232 devices and four types of
connectors.
DATA TERMINAL EQUIPMENT (DTE) (Most computers and terminals)
DATA COMMUNICATIONS EQUIPMENT (DCE) (Most modems and TNCs)
The connectors are DB9 and DB25, both male and female.
Most DTEs have male connectors (at least IBM PC's).
SIGNAL DEFINITIONS
DB9 DB25 Signal Purpose
1 PG Protective Ground: This is usually
the shield in a shielded cable. It
is designed to be connected to the
equipment frame and may be
connected to external grounds.
3 2 TxD Transmitted Data: Sourced by DTE, received
by DCE. Data terminal equipment cannot send
unless RTS, CTS, DSR and DTR are
asserted.
2 3 RxD Received Data: Received by the
DTE, sourced by DCE.
7 4 RTS Request to Send: Sourced by DTE,
. received by DCE. RTS is asserted by the DTE
when it wants to send data. The DCE
responds by asserting CTS.
8 5 CTS Clear to Send: Sourced by DCE, received by DTE.
CTS must be asserted before the DTE
can transmit data.
6 6 DSR Data Set Ready: Sourced by DCE, received by DTE.
Indicates that the DCE has made a
connection of the telephone line
and is ready to receive data. The
DTE must see this asserted before
it can transmit data.
5 7 SG Signal Ground: Ground reference
for the signal is separate from pin
1, protective ground.
1 8 DCD Data Carrier Detect: Sourced by
DCE, received by DTE. Indicates that a DCE has
detected the carrier on the
telephone line. Originally it was
used in half-duplex systems but can
used in full-duplex systems too.
4 20 DTR Data Terminal Ready: Sourced by DTE, received
by DCE. Indicates the DTE is ready
for sending or receiving.
9 22 RI Ring Indicator: Sourced by DCE, recieved by
DTE. Indicates that a ringing signal is
detected.
CABLING RS232 DEVICES
DTE devices can be connected directly to DCE. If two DTE devices
(two computers) are to be connected, a NULL modem (cross over
cable) is needed.
Here are some sample cables:
(-->-- Indicates the signal flow)
DB9 DTE Null Modem to DB9 DTE DB9 DTE ----- to ----- DB9 DCE
DTE DTE DTE DCE
RxD 2 --<--------<-- 3 TxD RxD 2 --<--------<-- 2 RxD
TxD 3 -->-------->-- 2 RxD TxD 3 -->-------->-- 3 TxD
Gnd 5 -------------- 5 Gnd Gnd 5 -------------- 5 Gnd
RTS 7 -->-------->-- 8 CTS RTS 7 -->-------->-- 7 RTS
CTS 8 --<--------<-- 7 RTS CTS 8 --<--------<-- 8 CTS
DB9 DTE Null Modem to DB25 DTE DB9 DTE ----- to ---- DB25 DCE
DTE DTE DTE DCE
RxD 2 --<--------<-- 2 TxD RxD 2 --<--------<-- 3 RxD
TxD 3 -->-------->-- 3 RxD TxD 3 -->-------->-- 2 TxD
Gnd 5 -------------- 7 Gnd Gnd 5 -------------- 7 Gnd
RTS 7 -->-------->-- 5 CTS RTS 7 -->-------->-- 4 RTS
CTS 8 --<--------<-- 4 RTS CTS 8 --<--------<-- 5 CTS
-LOOP Connection for CT
Make up identical Y-adapters with DB9 connectors to plug into
each computer. This scheme lets you use the normal Null Modem
cables you use for CT operation without the -LOOP option.
DB9 Female
At Computer
RxD 2 --<--------<-- 2 RxD DB9 Male
Gnd 5 ---|---------- 5 Gnd
|
|---------- 5 Gnd
TxD 3 -->-------->-- 3 TxD DB9 Male
RTS 7 --| RTS and CTS shorted
CTS 8 --|
73!
--
Dave Pascoe | mailto:dave@mathworks.com | Voice: 508.647.7362
KM3T | http://www.mathworks.com | FAX: 508.647.7002
PGP fingerprint: 53 AD 71 88 2F AA 45 AC D0 2E 68 91 71 77 39 AF
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