Author: Jicheng Training Network【Teacher Chen Sheng】
As industrial control personnel, it is necessary for us to understand these contents, which are very helpful for programming and data communication.RS-232, RS-422, and RS-485 are all serial data interface standards, originally formulated and published by the Electronic Industries Alliance (EIA): ★★★RS-232 was released in 1962, named EIA-232-E, as an industrial standard to ensure compatibility between products from different manufacturers.
★★★RS-422 was developed from RS-232 to address its shortcomings. To improve the short communication distance and low speed of RS-232, RS-422 defines a balanced communication interface, increasing the transmission speed to 10Mb/s, extending the transmission distance to 4000 feet (when the speed is below 100kb/s), and allowing up to 10 receivers to be connected on one balanced bus. RS-422 is a one-way, balanced transmission specification with single machine sending and multiple machines receiving, named TIA/EIA-422-A standard.
★★★To expand its application range, the EIA established the RS-485 standard in 1983 based on RS-422, adding multi-point, bidirectional communication capability, which allows multiple transmitters to connect to the same bus while increasing the transmitter’s driving capability and conflict protection features, extending the common mode range of the bus, later named TIA/EIA-485-A standard. Since the proposed standards by EIA all use “RS” as a prefix, it is still common in the communication industry to refer to the above standards with the RS prefix.
(1) Performance Parameter Table of RS-232, RS-422, and RS-485:
|
Specification |
RS-232 |
RS-422 |
RS-485 |
|
|
Working Mode |
Single-ended |
Differential |
Differential |
|
|
Number of Nodes |
1 Send, 1 Receive |
1 Send, 10 Receive |
1 Send, 32 Receive |
|
|
Maximum Transmission Cable Length |
15m (20m) |
1000m |
1000m |
|
|
Maximum Transmission Rate |
20Kb/S |
10Mb/s |
10Mb/s |
|
|
Maximum Driving Output Voltage |
+/-25V |
-0.25V～+6V |
-7V～+12V |
|
|
Driver Output Signal Level (Minimum Load) |
Load |
+/-5V～+/-15V |
+/-2.0V |
+/-1.5V |
|
Driver Output Signal Level (Maximum No Load) |
No Load |
+/-25V |
+/-6V |
+/-6V |
|
Driver Load Impedance (Ω) |
3K～7K |
100 |
54 |
|
|
Slew Rate (Maximum) |
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 |
|
|
Driver Common Mode Voltage |
-3V～+3V |
-1V～+3V |
||
|
Receiver Common Mode Voltage |
-7V～+7V |
-7V～+12V |
(2) Definitions of Simplex, Half-Duplex, and Full-DuplexIf at any moment during the communication process, information can only be transmitted from one party A to another party B, it is called simplex. If at any moment, information can be transmitted from A to B and also from B to A, but only one direction of transmission exists, it is called half-duplex transmission. If at any moment, there are bidirectional signal transmissions from A to B and from B to A on the line, it is called full-duplex.
|
——–> |
<——–> |
——–> |
|
A———B |
A———-B |
A———B |
|
<——– |
||
|
Simplex |
Half-Duplex |
Full-Duplex |
(3) Some Notes on RS-232Commonly used pins for RS-232 are 2, 3, and 5. Pin 5 is the ground, while pins 2 and 3 are used for data transmission. In practical use, two types of wiring sequences are used: straight-through and crossover for pins 2 and 3. The connectors for RS-232 can be divided into male (with pins) and female (with holes).
Jicheng Training: jcpeixun gathers the most comprehensive video tutorials and practical content on automation.
A learning and communication platform worth your attention!
National customer service QQ/Hotline: 4001114100
For more exciting content, click Read the Original!