Sun Microsystems, Inc.   Sun System Handbook - ISO 3.4 June 2011 Internal/Partner Edition
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Communication Troubleshooting

Electrical Characteristics
RS-232 Signals
RS-449 Signals

Electrical Characteristics

EIA RS-232-C Section 2.3

For data interchange circuits, the signal shall be considered in the marking condition when the voltage (V1) interchange circuit measured at the interface point, is more negative than minus three volts with respect to Circuit AB (Signal Ground). The signal shall be considered in the spacing condition when the voltage (V1) is more positive than plus three volts with respect to circuit AB. The signal state in not uniquely defined when the voltage (V1) is in this transition region.

EIA RS-232-D Section 2.1.3

For data interchange circuits, the signal shall be considered in the marking condition when the voltage (V1) on the interchange circuit, measured at the interface point, is more negative than minus three volts with respect to Circuit AB (Signal Ground). The signal shall be considered in the spacing condition when the voltage (V1) is more positive than plus three volts with respect to circuit AB. The region between plus three volts and minus three volts is defined as the transition region. The signal state in not uniquely defined when the voltage (V1) is in this transition region.

During the transmission of data, the marking condition shall be used to denote the binary state ONE and the spacing condition shall be used to denote state ZERO.

EIA RS-422-A Section 4.1.1

For either binary state, the magnitude of the differential voltage (V0) measured between the two generator output terminals shall not be less than 6.0 volts; nor shall the magnitude of V0a and V0b measured between the two generator output terminals and generator circuit ground be more than 6.0 volts.

EIA RS-423-A Section 4.1.1

For either binary state, the magnitude of the voltage (V0) measured between the generator output terminal and generator circuit ground shall not be less than 4.0 volts nor more than 6.0 volts. For the opposite binary state, the polarity of V0 shall be reversed.

EIA RS-449-A Section 2.1.1

The following circuits are classified as Category I circuits: SD, RD, TT, ST, RT, RS, CS, RR, TR, and DM.

For applications where the signaling rate on the data interchange circuits (Circuits SD and RD) is 20,000 bits per second or less, the individual Category I circuits shall use either the balanced electrical characteristics of RS-423, without the cable termination resistance (Rt), or the unbalanced electrical characteristics of RS-422-A. Two leads shall be brought out to the interface connector for each Category I circuit. Each interchange circuit consists of a pair of wires interconnecting a balanced or unbalanced generator and a differential receiver.

For applications where the signaling rate on the data interchange circuits (Circuits SD and RD) is above 20,000 bits per second, all Category I circuits shall use the balanced electrical characteristics of RS-422. Use of optional cable termination resistance (Rt) permitted. Each interchange circuit consists of a pair of wires interconnecting a balanced generator and a differential receiver.

EIA RS-449-A Section 2.1.2

All other circuits are classified as Category II circuits. For all applications, Category II circuits shall use the unbalanced electrical characteristics of RS-423. Each Category II interchange circuit consists of one wire interconnecting an unbalanced generator and a differential receiver.


RS-232 Signals

PIN SIGNAL SIGNAL NAME FLOW DESCRIPTION
2
14
BA
or
TD
Transmit Data Output Data transmitted to the data communications equipment.
3
16
BB
or
RD
Receive Data Input Data received from the data communications equipment.
4
19
CA
or
RTS
Request to Send Output Signal sent to the data communications equipment, asking if it is ready to start accepting data.
5
13
CB
or
CTS
Clear to Send Input Ready to accept data signal from the data communications equipment.
6 CC
or
DSR
Data Set Ready Input Data communications equipment indicates the status of the local data set.
7 AB
or
SG
Signal Ground None Signal Ground provides a reference level for the signal voltages.
8
12
CF
or
DCD
Data Carrier Detect Input Data communications equipment detected "carrier." Example: a modem senses tones sent to it by another modem over phone lines.
15 DB
or
TC
Transmit Clock
from DCE
Input Transmit clock from the modem. Usually not used for asynchronous devices (terminals, printers, and modems, etc.).
17 DD
or
RC
Receive Clock
from DCE
Input Receive clock from the modem. Usually not used for asynchronous devices (terminals, printers, and modems, etc.).
20 CD
or
DTR
Data Terminal
Ready
Output The DTE is powered on and ready to communicate as the "local data terminal" with the data communication equipment. For example, the modem.
24 DA
or
TCO
Transmit Clock
from DTE
Output Provides transmit clock from the DTE. Usually not used for asynchronous devices (terminals, printers, and modems, etc.).


RS-449 Signals

PIN SIGNAL SIGNAL NAME FLOW DESCRIPTION
4
22
SD
or
TD
Transmit Data Output Data transmitted to the data communications equipment.
6
24
RD Receive Data Input Data received from the data communications equipment.
7
25
RS
or
RTS
Request to Send Output Signal sent to the data communications equipment, asking if it is ready to start accepting data.
9
27
CS
or
CTS
Clear to Send Input Ready to accept data signal from the data communications equipment.
11
29
DM
or
DSR
Data Set Ready Input Data communications equipment indicates the status of the local data set.
19 SG Signal Ground None Signal Ground provides a reference level for the signal voltages.
13
31
RR
or
DCD
Data Carrier Detect Input Data communications equipment detected "carrier."
Example: a modem senses tones sent to it by another modem over phone lines.
5
23
ST
or
TC
Transmit Clock
from DCE
Input Transmit clock from the modem. Usually not used for asynchronous devices (terminals, printers, and modems, etc.).
8
26
RT
or
RC
Receive Clock
from DCE
Input Receive clock from the modem. Usually not used for asynchronous devices (terminals, printers, and modems, etc.).
12
30
TR
or
DTR
Data Terminal
Ready
Output The DTE is powered on and ready to communicate as the "local data terminal" with the data communication equipment. For example, the modem.
17
35
TT
or
TCO
Transmit Clock
from DTE
Output Provides transmit clock from the DTE. Usually not used for asynchronous devices (terminals, printers, and modems, etc.).

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