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Subsections


Cables

You can either use the cable that came with your UPS (the easiest if we support it) or you can make your own cable. We recommend that you obtain a supported cable directly from APC.

If you already have an APC cable, you can determine what kind it is by examining the flat sides of the two connectors where you will find the cable number embossed into the plastic. It is generally on one side of the male connector.

To make your own cable you must first know whether you have a UPS that speaks the apcsmart protocol or a ``dumb'' UPS that uses serial port line voltage signalling.

If you have an smart UPS, and you build your own cable, build a Smart-Custom cable. If you have a voltage-signalling or dumb UPS, build a Simple-Custom cable. If you have a BackUPS CS with a RJ45 connector, you can build your own Custom-RJ45 cable.


Smart-Custom Cable for SmartUPSes

       SMART-CUSTOM CABLE
     
     Signal Computer                  UPS
            DB9F                     DB9M
      RxD    2   --------------------  2  TxD  Send
      TxD    3   --------------------  1  RxD  Receive
      GND    5   --------------------  9  Ground

When using this cable with apcupsd specify the following in apcupsd.conf:

     UPSCABLE smart
     UPSTYPE apcsmart
     DEVICE /dev/ttyS0 (or whatever your serial port is)

If you have an OS that requires DCD or RTS to be set before you can receive input, you might try building the standard APC Smart 940-0024C cable listed below.


Simple-Custom Voltage-Signalling Cable for ``dumb'' UPSes

NOTE: YOU DO NOT HAVE THIS CABLE UNLESS YOU BUILT IT YOURSELF. THE SIMPLE-CUSTOM CABLE IS NOT AN APC PRODUCT.

For ``dumb'' UPSes using voltage signalling, if you are going to build your own cable, we recommend to make the cable designed by the apcupsd team as follows:

            SIMPLE-CUSTOM CABLE
     
     Signal Computer                  UPS
            DB9F   4.7K ohm          DB9M
      DTR    4   --[####]--*              DTR set to +5V by Apcupsd
                           |
      CTS    8   ----------*---------  5  Low Battery
      GND    5   --------------------  4  Ground
      DCD    1   --------------------  2  On Battery
      RTS    7   --------------------  1  Kill UPS Power

List of components one needs to make the Simple cable:

  1. One (1) male DB9 connector, use solder type connector only.
  2. One (1) female DB9/25F connector, use solder type connector only.
  3. One (1) 4.7K ohm 1/4 watt 5% resistor.
  4. resin core solder.
  5. three (3) to five (5) feet of 22AWG multi-stranded four or more conductor cable.

  1. Solder the resistor into pin 4 of the female DB9 connector.
  2. Next bend the resistor so that it connects to pin 8 of the female DB9 connector.
  3. Pin 8 on the female connector is also wired to pin 5 on the male DB9 connector. Solder both ends.
  4. Solder the other pins, pin 5 on the female DB9 to pin 4 on the male connector; pin 1 on the female connector to pin 2 on the male connector; and pin 7 on the female connector to pin 1 on the male connector.
  5. Double check your work.

We use the DTR (pin 4 on the female connector) as our +5 volts power for the circuit. It is used as the Vcc pull-up voltage for testing the outputs on any ``UPS by APC'' in voltage-signalling mode. This cable may not work on a BackUPS Pro if the default communications are in apcsmart mode. This cable is also valid for ``ShareUPS'' BASIC Port mode and is also reported to work on SmartUPSes. However, the Smart Cable described above is much simpler. To have a better idea of what is going on inside apcupsd, for the SIMPLE cable apcupsd reads three signals and sets three:

     Reads:
     CD, which apcupsd uses for the On Battery signal when high.
     
     CTS, which apcupsd uses for the Battery Low signal when high.
     
     RxD (SR), which apcupsd uses for the Line Down
         signal when high. This signal isn't used for much.
     
     Sets:
     DTR, which apcupsd sets when it detects a power failure (generally
          5 to 10 seconds after the CD signal goes high). It
          clears this signal if the CD signal subsequently goes low
          -- i.e. power is restored.
     
     TxD (ST), which apcupsd clears when it detects that the CD signal
          has gone low after having gone high - i.e. power is restored.
     
     RTS, which apcupsd sets for the killpower signal -- to cause the UPS
          to shut off the power.

Please note that these actions apply only to the SIMPLE cable, the signals used on the other cables are different.

Finally, here is another way of looking at the CUSTOM-SIMPLE cable:

     APCUPSD SIMPLE-CUSTOM CABLE
     
     Computer Side  |  Description of Cable           |     UPS Side
     DB9f  |  DB25f |                                 |   DB9m  | DB25m
     4     |   20   |  DTR (5vcc)             *below  |    n/c  |
     8     |    5   |  CTS (low battery)      *below  | <-  5   |   7
     2     |    3   |  RxD (no line voltage)  *below  | <-  3   |   2
     5     |    7   |  Ground (Signal)                |     4   |  20
     1     |    8   |  CD (on battery from UPS)       | <-  2   |   3
     7     |    4   |  RTS (kill UPS power)           | ->  1   |   8
     n/c   |    1   |  Frame/Case Gnd (optional)      |     9   |  22
     
     Note: the <- and -> indicate the signal direction.

When using this cable with apcupsd specify the following in apcupsd.conf:

     UPSCABLE simple
     UPSTYPE dumb
     DEVICE /dev/ttyS0 (or whatever your serial port is)


Custom-RJ45 Smart Signalling Cable for BackUPS CS Models

If you have a BackUPS CS, you are probably either using it with the USB cable that is supplied or with the 940-0128A supplied by APC, which permits running the UPS in dumb mode. By building your own cable, you can now run the BackUPS CS models (and perhaps also the ES models) using smart signalling and have all the same information that is available as running it in USB mode.

The jack in the UPS is actually a 10 pin RJ45. However, you can just as easily use a 8 pin RJ45 connector, which is more standard (ethernet TX, and ISDN connector). It is easy to construct the cable by cutting off one end of a standard RJ45-8 ethernet cable and wiring the other end (three wires) into a standard DB9F female serial port connector.

Below, you will find a diagram for the CUSTOM-RJ45 cable:

       CUSTOM-RJ45 CABLE
     
     Signal Computer              UPS     UPS
            DB9F                 RJ45-8  RJ45-10
      RxD    2   ----------------  1      2     TxD  Send
      TxD    3   ----------------  7      8     RxD  Receive
      GND    5   ----------------  6      7     Ground
      FG  Shield ----------------  3      4     Frame Ground
     
     The RJ45-8 pins are: looking at the end of the connector:
     
      8 7 6 5 4 3 2 1
     ___________________
     | . . . . . . . . |
     |                 |
     -------------------
            |____|
     
     The RJ45-10  pins are: looking at the end of the connector:
     
     10 9 8 7 6 5 4 3 2 1
     _______________________
     | . . . . . . . . . . |
     |                     |
     -----------------------
            |____|

For the serial port DB9F connector, the pin numbers are stamped in the plastic near each pin. In addition, there is a diagram near the end of this chapter.

Note, one user, Martin, has found that if the shield is not connected to the Frame Ground in the above diagram (not in our original schematic), the UPS (a BackUPS CS 500 EI) will be unstable and likely to rapidly switch from power to batteries (i.e. chatter).

When using this cable with apcupsd specify the following in apcupsd.conf:

     UPSCABLE smart
     UPSTYPE apcsmart
     DEVICE /dev/ttyS0 (or whatever your serial port is)

The information for constructing this cable was discovered and transmitted to us by slither_man. Many thanks!


Other APC Cables that apcupsd Supports

apcupsd will also support the following off the shelf cables that are supplied by APC


Voltage Signalling Features Supported by Apcupsd for Various Cables

The following table shows the features supported by the current version of apcupsd for various cables running the UPS in voltage-signalling mode.

Cable Power Loss Low Battery Kill Power Cable Disconnected
940-0020B Yes No Yes No
940-0020C Yes Yes Yes No
940-0023A Yes No No No
940-0119A Yes Yes Yes No
940-0127A Yes Yes Yes No
940-0128A Yes Yes Yes No
940-0095A/B/C Yes Yes Yes No
simple Yes Yes Yes No


Voltage Signalling

Apparently, all APC voltage-signalling UPSes with DB9 serial ports have the same signals on the output pins of the UPS. The difference at the computer end is due to different cable configurations. Thus, by measuring the connectivity of a cable, one can determine how to program the UPS.

The signals presented or accepted by the UPS on its DB9 connector using the numbering scheme listed above is:

     UPS Pin         Signal meaning
      1     <-     Shutdown when set by computer for 1-5 seconds.
      2     ->     On battery power (this signal is normally low but
                         goes high when the UPS switches to batteries).
      3     ->     Mains down (line fail) See Note 1 below.
      5     ->     Low battery. See Note 1 below.
      6     ->     Inverse of mains down signal. See Note 2 below.
      7     <-     Turn on/off power (only on advanced UPSes only)
     
      Note 1: these two lines are normally open, but close when the
          appropriate signal is triggered. In fact, they are open collector
          outputs which are rated for a maximum of +40VDC and 25 mA. Thus
          the 4.7K ohm resistor used in the Custom Simple cable works
          quite well.
     
      Note 2: the same as note 1 except that the line is normally closed,
          and opens when the line voltage fails.


The Back-UPS Office 500 signals

The Back-UPS Office UPS has a telephone type jack as output, which looks like the following:

     Looking at the end of the connector:
     
        6 5 4 3 2 1
       _____________
      | . . . . . . |
      |             |
      |  |----------|
      |__|

It appears that the signals work as follows:

       UPS            Signal meaning
     1 (brown)    <-   Shutdown when set by computer for 1-5 seconds.
     2 (black)    ->   On battery power
     3 (blue)     ->   Low battery
     4 (red)           Signal ground
     5 (yellow)   <-   Begin signalling on other pins
     6 (none)          none


Analyses of APC Cables

940-0020B Cable Wiring:

Although we do not know what the black box semi-conductor contains, we believe that we understand its operation (many thanks to Lazar M. Fleysher for working this out).

This cable can only be used on voltage-signalling UPSes, and provides the On Battery signal as well as kill UPS power. Most recent evidence (Lazar's analysis) indicates that this cable under the right conditions may provide the Low Battery signal. This is yet to be confirmed.

This diagram is for informational purposes and may not be complete, we don't recommend that use it to build you build one yourself.

     APC Part# - 940-0020B

     Signal Computer                  UPS
            DB9F                     DB9M
      CTS    8   --------------------  2  On Battery
      DTR    4   --------------------  1  Kill power
      GND    5   ---------------*----  4  Ground
                                |
                     ---        *----  9  Common
      DCD    1  ----|///|-----------   5  Low Battery
                    |\\\|
      RTS    7  ----|///| (probably a
                     ---   semi-conductor)

940-0020C Cable Wiring:

This cable can only be used on voltage-signalling UPSes, and provides the On Battery signal, the Low Battery signal as well as kill UPS power. You may specify UPSCABLE 940-0020C.

This diagram is for informational purposes and may not be complete, we don't recommend that use it to build you build one yourself.

     APC Part# - 940-0020C

     Signal Computer                  UPS
            DB9F                     DB9M
      CTS    8   --------------------  2  On Battery
      DTR    4   --------------------  1  Kill power
      GND    5   ---------------*----  4  Ground
                                |
                                *----  9  Common
      RTS    7 -----[ 93.5K ohm ]----- 5  Low Battery
                    or semi-conductor

940-0023A Cable Wiring:

This cable can only be used on voltage-signalling UPSes, and apparently only provides the On Battery signal. As a consequence, this cable is pretty much useless, and we recommend that you find a better cable because all APC UPSes support more than just On Battery. Please note that we are not sure the following diagram is correct.

This diagram is for informational purposes and may not be complete, we don't recommend that use it to build you build one yourself.

     APC Part# - 940-0023A
     
     Signal Computer                  UPS
            DB9F                     DB9M
      DCD    1   --------------------  2  On Battery
     
                   3.3K ohm
      TxD    3   --[####]-*
                          |
      DTR    4   ---------*
      GND    5   ---------------*----  4  Ground
                                |
                                *----  9  Common

940-0024C Cable Wiring:

If you wish to build the standard cable furnished by APC (940-0024C), use the following diagram.

     APC Part# - 940-0024C
     
     Signal Computer                  UPS
            DB9F                     DB9M
      RxD    2   --------------------  2  TxD  Send
      TxD    3   --------------------  1  RxD  Receive
      DCD    1   --*
                   |
      DTR    4   --*
      GND    5   --------------------  9  Ground
      RTS    7   --*
                   |
      CTS    8   --*

940-0095A Cable Wiring:

This is the definitive wiring diagram for the 940-0095A cable submitted by Chris Hanson, who disassembled the original cable, destroying it in the process. He then built one from his diagram and it works perfectly.

     APC Part# - 940-0095A

     UPS end                                      Computer end
     -------                                      ------------
                       47k        47k
     BATTERY-LOW (5) >----R1----*----R2----*----< DTR,DSR,CTS (4,6,8)
                              |          |
                              |          |
                              |         /  E
                              |       |/
                              |    B  |
                              *-------|  2N3906 PNP
                                      |
                                      |\
                                        \  C
                                         |
                                         |
                                         *----< DCD (1)     Low Batt
                                         |
                                         |
                                         R 4.7k
                                         3
                                         |
                                  4.7k   |
     SHUTDOWN (1)    >----------*----R4----*----< TxD (3)
                              |
                              |  1N4148
                              *----K|---------< RTS (7)      Shutdown
     
     POWER-FAIL (2)  >--------------------------< RxD,RI (2,9) On Batt
     
     GROUND (4,9)    >--------------------------< GND (5)

Operation:

940-0095B Cable Wiring:

This diagram is for informational purposes and may not be complete, we don't recommend that use it to build you build one yourself.

     APC Part# - 940-0095B
     
     Signal Computer                  UPS
            DB9F                     DB9M
      DTR    4   ----*
      CTS    8   ----|
      DSR    6   ----|
      DCD    1   ----*
      GND    5   ---------------*----  4  Ground
                                |
                                *----  9  Common
      RI     9   ----*
                     |
      RxD    2   ----*---------------  2  On Battery
      TxD    3   ----------[####]----  1  Kill UPS Power
                           4.7K ohm

940-0119A Cable Wiring:

This diagram is for informational purposes and may not be complete, we don't recommend that use it to build you build one yourself.

     APC Part# - 940-0119A
     
       UPS      Computer
       pins     pins      Signal             Signal meaning
     1 (brown)    4,6      DSR DTR     <-   Shutdown when set by computer for 1-5 seconds.
     2 (black)    8,9      RI  CTS     ->   On battery power
     3 (blue)     1,2      CD  RxD     ->   Low battery
     4 (red)       5       Ground
     5 (yellow)    7       RTS         <-   Begin signalling on other pins
     6 (none)     none

Serial BackUPS ES Wiring:

The BackUPS ES has a straight through serial cable with no identification on the plugs. To make it work with apcupsd, specify the UPSCABLE 940-0119A and UPSTYPE backups. The equivalent of cable 940-0119A is done on a PCB inside the unit.

     computer           ----------- BackUPS-ES -----------------
     DB9-M              DB-9F
     pin    signal      pin
     
      4      DSR   ->    4 --+
                             |  diode   resistor
      6      DTR   ->    6 --+---->|----/\/\/\---o kill power
     
      1      DCD   <-    1 --+
                             |
      2      RxD   <-    2 --+----------------+--o low battery
                                              |
      7      RTS   ->    7 --------+--/\/\/\--+
                                   |
                                   +--/\/\/\--+
                                              |
      8      RI    <-    8 --+----------------+--o on battery
                             |
      9      CTS   <-    9 --+
     
      5      GND   ---   5 ----------------------o ground
     
      3      TxD         3 nc

940-0128A Cable Wiring:

Though these UPSes are USB UPSes, APC supplies a serial cable (typically with a green DB9 F connector) that has 940-0128A stamped into one side of the plastic serial port connector. The other end of the cable is a 10 pin RJ45 connector that plugs into the UPS (thanks to Dean Waldow for sending a cable!). Apcupsd version 3.8.5 and later supports this cable when specified as UPSCABLE 940-0128A and UPSTYPE dumb. However, running in this mode much of the information that would be available in USB mode is lost. In addition, when apcupsd attempts to instruct the UPS to kill the power, it begins cycling about 4 times a second between battery and line. The solution to the problem (thanks to Tom Suzda) is to unplug the UPS and while it is still chattering, press the power button (on the front of the unit) until the unit beeps and the chattering stops. After that the UPS should behave normally and power down 1-2 minutes after requested to do so.

Thanks to all the people who have helped test this and have provided information on the cable wiring, our best guess for the cable schematic is the following:

     APC Part# - 940-0128A

     computer      --------- Inside the Connector---------  UPS
     DB9-F         |                                     |  RJ45
     pin - signal  |                                     |  Pin - Color
                   |                                     |
      4     DSR  ->|---+                                 |
                   |   |  diode   resistor               |
      6     DTR  ->|---+---->|----/\/\/\---o kill power  |  8  Orange
                   |                                     |
      1     DCD  <-|----+                                |
                   |    |                                |
      2     RxD  <-|----+----------------+--o low battery|  3  Brown
                   |                     |               |
      7     RTS  ->|----------+--/\/\/\--+               |
                   |          |                          |
                   |          +--/\/\/\--+               |
                   |                     |               |
      8     RI   <-|----+----------------+--o on battery |  2  Black
                   |    |                                |
      9     CTS  <-|----+                                |
                   |                         signal      |
      5     GND  --|-----------------------o ground      |  7  Red
                   |                                     |
      3     TxD    |                                     |
                   |                         chassis     |
      Chassis/GND  |-----------------------o ground      |  4  Black
                   |                                     |
                   |          Not connected              |  1, 5, 6, 9, 10
                   --------------------------------------
     
     The RJ45 pins are: looking at the end of the connector:
     
     10 9 8 7 6 5 4 3 2 1
     _______________________
     | . . . . . . . . . . |
     |                     |
     -----------------------
            |____|

940-0128D Cable Wiring:

940-0128D is functionally similar to the 940-0128A cable except for NC on (6) DTR and (2) RD on the computer side.

Unverified: Try setting apcupsd to UPSTYPE dumb and UPSCABLE 940-0128A.

     APC Part# - 940-0128D
     
     DB9(Computer)               RJ45-10(UPS)
     
      (5)     (1)                 ____________
     ( o o o o o )               [ oooooooooo ]
      \ o o o o /                [____________]
       (9)   (6)                 (10)  [_]  (1)
     
     
      RI(9)<---+
               |
     CTS(8)<---+--- E   2N2222(NPN)
                     \|___
                ____ /| B |
               |    C     |
               |          |
               +---vvvv---+--[>|------<(2)OnBatt
     RTS(7)>---|    2k      1N5819
               +---vvvv---+--[>|------<(3)LowBatt
               |          |
               +--- C     |
                     \|___|
                     /| B
     DCD(1)<------- E    2N2222(NPN)
     
     DTR(4)>-------------------------->(8)KillPwr
     
     GND(5)----------------------------(7)Signal GND
     (Shield)--------------------------(4)Chassis GND

940-0127B Cable Wiring:

Standard USB cable for USB-capable models with 10-pin RJ45 connector.

     APC Part# - 940-0127B

     USB(Computer)      RJ45-10(UPS)
      _________          ____________
     | = = = = |        [ oooooooooo ]
     |_________|        [____________]
      (1)   (4)         (10)  [_]  (1)
     
       +5V(1)-----------(1)+5V
     DATA+(2)-----------(9)DATA+
     DATA-(3)-----------(10)DATA-
       GND(4)-----------(7)Signal GND
     (Shield)-----------(4)Chassis GRND


Win32 Implementation Restrictions for Simple UPSes

Due to inadequacies in the Win32 API, it is not possible to set/clear/get all the serial port line signals. apcupsd can detect: CTS, DSR, RNG, and CD. It can set and clear: RTS and DTR.

This imposes a few minor restrictions on the functionality of some of the cables. In particular, LineDown on the Custom Simple cable, and Low Battery on the 0023A cable are not implemented.


Internal Apcupsd Actions for Simple Cables

     
     This section describes how apcupsd 3.8.5 (March 2002)
     treats the serial port line signals for simple cables.
     
     apcaction.c:
      condition = power failure detected
      cable = CUSTOM_SIMPLE
      action = ioctl(TIOCMBIS, DTR)      set DTR (enable power bit?)
     
     apcaction.c:
      condition = power back
      cable = CUSTOM_SIMPLE
      action = ioctl(TIOCMBIC, DTR)      clear DTR (clear power bit)
      action = ioctl(TIOCMBIC, ST)       clear ST (TxD)
     
     apcserial.c:
      condition = serial port initialization
      cable = 0095A, 0095B, 0095C
      action = ioctl(TIOMBIC, RTS)       clear RTS (set PnP mode)
     
      cable = 0119A, 0127A, 0128A
      action = ioctl(TIOMBIC, DTR)       clear DTR (killpower)
      action = ioctl(TIOMBIS, RTS)       set   RTS (ready to receive)
     
     apcserial.c:
      condition = save_dumb_status
      cable = CUSTOM_SIMPLE
      action = ioctl(TIOMBIC, DTR)       clear DTR (power bit?)
      action = ioctl(TIOMBIC, RTS)       clear RTS (killpower)
     
      cable = 0020B, 0020C, 0119A, 0127A, 0128A
      action = ioctl(TIOMBIC, DTR)       clear DTR (killpower)
     
      cable = 0095A, 0095B, 0095C
      action = ioctl(TIOMBIC, RTS)       clear RTS (killpower)
      action = ioctl(TIOMBIC, CD)        clear DCD (low batt)
      action = ioctl(TIOMBIC, RTS)       clear RTS (killpower) a second time!
     
     apcserial.c:
      condition = check_serial
     
      cable = CUSTOM_SIMPLE
      action = OnBatt = CD
      action = BattLow = CTS
      action = LineDown = SR
     
      cable = 0020B, 0020C, 0119A, 0127A, 0128A
      action = OnBatt = CTS
      action = BattLow = CD
      action = LineDown = 0
     
      cable = 0023A
      action = Onbatt = CD
      action = BattLow = SR
      action = LineDown = 0
     
      cable = 0095A, 0095B, 0095C
      action = OnBatt = RNG
      action = BattLow = CD
      action = LineDown = 0
     
     
     apcserial.c
      condition = killpower
     
      cable = CUSTOM_SIMPLE, 0095A, 0095B, 0095C
      action = ioctl(TIOMCBIS, RTS)      set RTS (kills power)
      action = ioctl(TIOMCBIS, ST)       set TxD
     
      cable = 0020B, 020C, 0119A, 0127A, 0128A
      action = ioctl(TIOMCBIS, DTR)      set DTR (kills power)


RS232 Wiring and Signal Conventions

DB-25 Pin # DB-9 Pin # Name DTE-DCE Description
1 -- FG - Frame Ground/Chassis GND
2 3 TD -> Transmitted Data, TxD
3 2 RD <- Received Data, RxD
4 7 RTS -> Request To Send
5 8 CTS <- Clear To Send
6 6 DSR <- Data Set Ready
7 5 SG --- Signal Ground, GND
8 1 DCD <- Data Carrier Detect
9 -- -- - Positive DC test voltage
10 -- -- - Negative DC test voltage
11 -- QM <- Equalizer mode
12 -- SDCD <- Secondary Data Carrier Detect
13 -- SCTS <- Secondary Clear To Send
14 -- STD -> Secondary Transmitted Data
15 -- TC <- Transmitter (signal) Clock
16 -- SRD <- Secondary Receiver Clock
17 -- RC -> Receiver (signal) Clock
18 -- DCR <- Divided Clock Receiver
19 -- SRTS -> Secondary Request To Send
20 4 DTR -> Data Terminal Ready
21 -- SQ <- Signal Quality Detect
22 9 RI <- Ring Indicator
23 -- -- -> Data rate selector
24 -- -- <- Data rate selector
25 -- TC <- Transmitted Clock


Pin Assignment for the Serial Port (RS-232C), 25-pin and 9-pin, Female End

     
        13                         1         5         1
      _______________________________      _______________
      \  . . . . . . . . . . . . .  /      \  . . . . .  /    RS232-connectors
       \  . . . . . . . . . . . .  /        \  . . . .  /     looking into the
        ---------------------------          -----------      end of the cable.
        25                      14            9       6
     
     The diagram above represents the Female end of the cable. The
     male end is the same, but looking from inside the cable.
     
      DTE : Data Terminal Equipment (i.e. computer)
      DCE : Data Communications Equipment (i.e. UPS)
      RxD : Data received; 1 is transmitted "low", 0 as "high"
      TxD : Data sent; 1 is transmitted "low", 0 as "high"
      DTR : DTE announces that it is powered up and ready to communicate
      DSR : DCE announces that it is ready to communicate; low=modem hang-up
      RTS : DTE asks DCE for permission to send data
      CTS : DCE agrees on RTS
      RI  : DCE signals the DTE that an establishment of a connection is attempted
      DCD : DCE announces that a connection is established


Ioctl to RS232 Correspondence

     
     #define TIOCM_LE        0x001
     #define TIOCM_DTR       0x002
     #define TIOCM_RTS       0x004
     #define TIOCM_ST        0x008
     #define TIOCM_SR        0x010
     #define TIOCM_CTS       0x020
     #define TIOCM_CAR       0x040
     #define TIOCM_RNG       0x080
     #define TIOCM_DSR       0x100
     #define TIOCM_CD        TIOCM_CAR
     #define TIOCM_RI        TIOCM_RNG
     #define TIOCM_OUT1      0x2000
     #define TIOCM_OUT2      0x4000


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2009-03-11