Author: David Maden
Phone: +41 56 310 3616
Updated: 31.1.2008
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RS-232 Information
This is a simple note which attempts to collect together some of the folklore
associated with RS-232 serial connections between computers and devices.
It is currently a simple text document ... sorry!
Contents
--------
1. Electrical Standards
2. DB9 IBM PC COM1 port
3. DB25 Connector
4. RJ45 Connectors
5. Adapters
6. Abbreviations
7. References
1. Electrical Standards
--------------------
RS232 Signals are between +12V and -12V and are "Active Low".
Signal = 0 (LOW) > +3V
Signal = 1 (HIGH) < -3V
2. DB9M IBM PC COM1 Port This is probably the de facto "Standard"
---------------------
DTE Connector DB9 Male
1 2 3 4 5 6 7 8 9
DCD RxD TxD DTR GND DSR RTS CTS RI
Front view of male DB9 connector:
1 5
+-------------+
\ o o o o o /
\ o o o o /
+-------+
6 9
3. DB25 Connector
--------------
When RS-232 electrical signals are terminated in a DB25 pin connector, the standard
is called RS-232-C.
DTE Connector DB25 Male
1 2 3 4 5 6 7 8 9 10 11 12 13
SHLD TxD RxD RTS CTS DSR GND DCD - - - SDCD SCTS
14 15 16 17 18 19 20 21 22 23 24 25
STD DB SRD RCLK LL SRTS DTR RL/SQ RI CH/CI ACLK -
Front view of male DB25 connector:
1 13
+-----------------------------+
\ o o o o o o o o o o o o o /
\ o o o o o o o o o o o o /
+-----------------------+
14 25
4. RJ45 Connectors
---------------
Note: RJ45 sockets have can have 10 pins. The RJ45 cable connectors at PSI have
8 pins. The numbering here is for these 8 pins. Sorry if this leads
to confusion.
i) RS-232D or EIA/TIA-561 (From www.zytrax.com/tech/layer_1/cables/tech_rs232.htm)
1 2 3 4 5 6 7 8
DSR/RI DCD DTR GND RxD TxD CTS RTS
ii) ??? (From www.cisco.com/univercd/cc/td/doc/product/ipvc/ipvc3540/mcu_mod/rel_1_0/appb.htm)
1 2 3 4 5 6 7 8
TxD- TxD+ RxD+ GND RxD-
iii) MVME2300 and MVME5100 (the usual SLS VME IOCs) "Debug" Connectors
The Motorola MVME2300 and MVME5100 are the usual single board
computers in use at SLS for providing EPICS control (IOC) of VME crates.
This information is taken from the Motorola manual:
V2300A/IH4 MVME2300 Series VME Processor Module Installation and Use
which can be found at:
http://mcg.motorola.com/cfm/templates/documentation.cfm?\
PageID=0&ProductID=9&PageTypeID=4
1 2 3 4 5 6 7 8
DCD RTS GND TxD RxD GND CTS DTR
iv) Digi Portserver (EtherLite)
See ./Portserver-RJ45.gif and
ftp://ftp1.digi.com/support/documentation/9028700c.pdf.
1 2 3 4 5 6 7 8
DSR RTS SHLD TxD RxD SG CTS DTR
v) The SLS "PSI V2.1" RJ45 Connectors
The "PSI V2.1" is a SCSI/RJ45 adapter for the TEWS TIP866 8-channel serial
industry pack. The TIP866 is mounted in a Hytec 8002 carrier board with a
VTB8304 "straight-through" transition module. The transition module and the
"PSI V2.1" are connected via a SCSI cable and the result is 8 RJ45 connectors.
1 2 3 4 5 6 7 8
CTS DCD RxD GND GND TxD DTR RTS
vi) Lantronix Terminal Server (and NTI Serial Port Switch)
1 2 3 4 5 6 7 8
RTS DTR Tx+ Tx- Rx- Rx+ DSR CTS
Front view of RJ45 cable connector:
/ /
/ //
/ //
+-----------------+
/ /|
/ / |
+-----------------+ |
| ' ' ' ' ' ' ' ' | /
| 8 1 |/
+-----------------+
| |/
+--+-+--+
+-+
5. Adapters
--------
i) FA770 Blackbox RJ45/DB25M Adapter
This is labelled "Terminal Server"
DB25 Male
/----------- 2
RJ45 /-------------/------------ 3
/ / /-------- 4
1 ------------/-------------/----/--------- 5
2 -----\ / / / 6
3 ------\---/ /--------/----/----------- 7
4 --+ \------/--------/----/------------ 8
5 --+----------/ / / 9
6 ---------------------/ /
7 -------------------------/-----\
8 ------------------------/ \------- 20
ii) RJ45/DB9F Adapter with Label "MV2306 Cons"
MVME2300 DB9 Female
Signals
| /------------------------- 1
| / /-------------------- 2
V RJ45 / / /------------------ 3
/ / / -- 4
DCD 1 -----------/-----/--/----\ /---------- 5
RTS 2 ----------/-----/--/---\ \--/----------- 6
GND 3 ---------/-----/--/---------/ /------- 7
TxD 4 --------/-----/ / \------/-------- 8
RxD 5 -------/--------/ / -- 9
6 -- / /
CTS 7 -----/-----------------------/
DTR 8 ----/
iii) DB25 to DB9 Adapters, DB25M/DB9F and DB25F/DB9M
See ./DB25-DB9.gif
6. Abbreviations
-------------
ACLK Auxiliary Clock (a.k.a. DA)
CH/CI Signal Rate selector
CTS Clear to Send
DA Auxiliary Clock (a.k.a. ACLK)
DB Transmit Clock (a.k.a TCLK, TxCLK)
DCD Data Carrier Detect (a.k.a RLSD)
DCE Data Communications Equipment (i.e. Modem)
DD Receive Clock (a.k.a. RCLK)
DTE Data Terminal Equipment (i.e. PC or Device)
DSR Data Set Ready
DTR Data Terminal Ready
GND Signal Ground
LL Local Loopback
RCLK Receive Clock (a.k.a. DD)
RI Ring Indicator
RL Remote loopback
RLSD Received Line Signal Detect (a.k.a DCD)
RTS Request to Send
RxD Receive Data
SCTS Secondary Clear to send
SDCD Secondary Carrier Detect
SHLD Shield Ground
SQ Signal Quality Detector
SRD Secondary Receive Data
SRTS Secondary Request to Send
STD Secondary Transmit Data
TCLK Transmit Clock (a.k.a DB, TxCLK)
TxCLK Transmit Clock (a.k.a DB, TCLK)
TxD Transmit Data
7. References
----------
ZyTrax Tech ... a nicely written set of WWW pages with some useful information. The
following reference is to their "RS232 Wiring" page.
http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm
SSV Embedded Systems ... one of their products:
http://www.ssv-embedded.de/ssv/pc104/p98.htm
Cisco Cable Connectors:
http://www.cisco.com/univercd/cc/td/doc/product/ipvc/ipvc3540/mcu_mod/rel_1_0/appb.htm
Motorola MVME2300 Documentation
http://mcg.motorola.com/cfm/templates/documentation.cfm?\
PageID=0&ProductID=9&PageTypeID=4
NTI, Network Technologies Inc ... good diagrams of many different connectors.
http://www.networktechinc.com/technote.html
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