What is the RS-232-C interface? What is the characteristics of the RS-232-C interface? How is the length of the transmission cable consideration?
A: The data transfer between the computer and the computer or computer and the terminal can adopt two ways of serial communication and parallel communication. Since the serial communication method has less lines, low cost, especially during remote transmission, avoiding the inconsistency of multiple line characteristics is widely adopted. When serial communication, both parties require communication to use a standard interface to make different devices can easily connect to communications. The RS-232-C interface (also known as EIA RS-232-C) is the most commonly used serial communication interface. It is a standard for serial communication using the US Electronics Industry Association (EIA) combined with Bell system, modem manufacturers and computer terminal manufacturers. Its full name is "Data Terminal Device (DTE) and Data Communication Equipment (DCE) Standards" This standard specified that a 25 foot DB25 connector is used, each of the connector The signal content of the foot is specified, and the level of various signals is also specified.
(1) The signal content of the interface actually has many of the 25 leads of the RS-232-C, which is rarely used, generally only 3-9 leads in the computer and terminal communication. The signal contents of the 9 leads in RS-232-C are shown in Schedule 1
(2) The electrical characteristics of the interface are negative logic relationships in any signal lines in RS-232-C. That is: logic "1", - 5--15V; logic "0" 5- 15V. The noise tolerance is 2V. That is, the receiver is required to identify the signal as low as 3V as a logic "0", high to -3V as a logic "1" Schedule 1.
Pin serial number
Signal name
symbol
Flow
Features
2
send data
TXD
DTE → DCE
DTE sends a serial data
3
Receive data
RXD
DTE ← DCE
DTE receives serial data
4
Request to send
RTS
DTE → DCE
DTE request DCE switches the line to send mode
5
Allowed to send
CTS
DTE ← DCE
DCE tells the DTE line to send data
6
Data equipment is ready
DSR
DTE ← DCE
DCE is ready
Seduce
Signal ground
Publicly
8
Carrier detection
DCD
DTE ← DCE
Indicates that the DCE receives the remote carrier
20
Data terminal is ready
DTR
DTE → DCE
DTE is ready
twenty two
Ringing indication
Ri
DTE ← DCE
Indicates that the DCE is connected to the line, the ringing
(3) The physical structure of the interface The RS-232-C interface connector typically uses a 25-core inserted seat of DB-25, usually in the DCE end, and the socket is in the DTE end. Some equipment connected to the PC RS-232- C Interface, because the transfer control signal of the other party is not used, only three interface lines, "send data", "reception data", and "signal ground". Therefore, the 9-core socket of DB-9 is used, and the transmission line is shielded twisted.
(4) The length of the transmission cable is specified by the RS-232C standard in the case where the symbol distortion is less than 4%, and the length of the transmission cable should be 50 feet. In fact, this 4% symbol distortion is very conservative, in practical applications, about There are 99% of users working in the range of 10-20% in the symbol distortion, so the maximum distance in actual use will be far more than 50 feet. The US DEC has stipulated that the symbol distortion is 10% to the Scope 2 Experimental results. Among them, the cable is a shielded cable, and there are three pairs of twisted pairs in Decp.9107723, each of which consists of 22 # AWG, which is covered with a shielded network. The 2nd cable is no shielded cable. Model is DECP.NO.9105856-04 is a 22 # AWG four-core cable. Schedule 2 DEC's experimental results
Baud rate
Cable transmission distance (foot)
2 cable transmission distance (foot)
110
5000
3000
300
5000
3000
1200
3000
3000
2400
1000
500
4800
1000
250
9600
250
250
2. What is the RS-485 interface? Is it characterized than the RS-232-C interface?
A: Because the RS-232-C interface standard is earlier, it is inevitable that there is shortcomings, mainly the following four points:
(1) The signal level value of the interface is high, and the chip of the interface circuit is easily damaged, but the level conversion circuit can be connected to the TTL circuit due to the non-compatibility of the TTL level.
(2) The transmission rate is low. When asynchronous transmission, the baud rate is 20 kbps.
(3) The interface uses a signal line and a signal return line to constitute a common land, which is easy to generate common mode interference, so the anti-noise interference is weak.
(4) The transmission distance is limited, the maximum transmission distance is 50 feet, which is actually only about 50 meters.
In response to the shortcomings of RS-232-C, some new interface criteria have emerged, and RS-485 is one of them, it has the following features:
1. Electrical characteristics of RS-485: Logic "1" is represented by (2-6) V in two wires; the logic "0" is represented by the voltage difference between the two-wire. . The interface signal level is reduced by RS-232-C, which is not easily damaged by the chip of the interface circuit, and the level is compatible with the TTL level, which is convenient to connect to the TTL circuit.
2. The data maximum transmission rate of RS-485 is 10Mbps
3. The RS-485 interface is a combination of balancing drivers and differential receivers, and the anti-co-molding capability is enhanced, i.e., anti-noise interference.
4. The maximum transmission distance of the RS-485 interface is 4,000 feet. It can actually reach 3000 meters, and the RS-232-C interface is only allowed to connect to 1 transceiver on the bus, that is, single-stop capabilities. The RS-485 interface is allowed to connect to up to 128 transceivers on the bus. That is, it has multi-station capability so that users can easily establish a device network using a single RS-485 interface.
Because the RS-485 interface has good anti-noise interference, long transmission distance, and multi-station capabilities such as the preferred serial interface. Because the half-duplex network consisting of the RS485 interface, only two wiring is generally required, so the RS485 interface is transmitted with shielded twisted pair. The RS485 interface connector uses a 9-core block of DB-9, using DB-9 (holes) with the intelligent terminal RS485 interface, and the keyboard interface RS485 connected to the keyboard uses DB-9 (needle).
3. When using the RS485 interface, how is the length of the transfer cable consideration?
A: When using the RS485 interface, for a specific transmission line, the maximum cable length allowed from generator to load its data signal transmission is a function of the data signal rate, which is mainly limited by signal distortion and noise. . The relationship between the maximum cable length and signal rate shown below is to use a 24AWG copper core double-stranded telephone cable (0.51mm wire diameter), and the lineary capacitance is 52.5pf / m, the terminal load resistance is 100 o'clock. Out. (Curve lead from Appendix A) of GB11014-89. As can be seen from the figure, when the data signal signal is lowered below 90kbit / s, it is assumed that the maximum allowable signal loss is 6 dBV, the cable length is limited to 1200m. In fact, the curve in the figure is conservative, and it can be used in real time to obtain a cable length than it. When using cables of different lines. The maximum cable length obtained is different. For example, when the data signal rate is 600kbit / s, the 24AWG cable is used, and the maximum cable length is 200m by the figure. If the 19AWG cable (0.91 mm is used), the cable length will be greater than 200m; if the 28AWG cable ( The wire diameter is 0.32 mm), the cable length can only be less than 200m. Electrical parameters
Regulate
RS232
RS422
R485
Way of working
Single-ended
difference
difference
Node number
1 received, 1
1 send 10 receipts
1 hair 32
Maximum transmission cable length
50 feet
400 feet
400 feet
Maximum transmission rate
20kb / s
10MB / s
10MB / s
Maximum drive output voltage
/- 25V
-0.25V ~ 6V
-7V ~ 12V
Drive output signal level (load minimum)
load
/- 5V ~ /- 15V
/- 2.0V
/- 1.5V
Drive output signal level (no load max)
Empty
/- 25V
/- 6V
/- 6V
Drive load impedance (Ω)
3K ~ 7K
100
54
摆 rate (max)
30V / μs
N / a
N / a
Receiver input voltage range
/- 15V
-10V ~ 10V
-7V ~ 12V
Receiver input threshold
/- 3V
/- 200mv
/- 200mv
Receiver input resistance (Ω)
3K ~ 7K
4K (minimum)
≥12K
Drive common mode voltage
-3V ~ 3V
-1V ~ 3V
Receiver common mode voltage
-7V ~ 7V
-7V ~ 12V
Table 1
The above is some information I have organized in the learning process, I hope to help beginners. The RS485-232 converter pay special attention to the voltage problem. A module with active power is generally used. Moreover, the input voltage must be sufficient, otherwise the output signal is located in the blurred region due to the on-site interference, so that the level of the computer recognition or the output signal is erroneous.
