Working principles of RS485

These are the working principles of RS485. When we talk about the RS485 we first need to know that is stands for the “Recommended Standard no. 485” and that it is the serial communication standard which was established in 1998. The standard is used in many industrial equipment as the signal can be sent far and can still be sent simultaneously at multiple points. This uses Half duplex communication meaning that it can only send information in one direction at a time.

Working principles of RS485

The principle works by voltage changes as can be seen below:

• When V _a – V _b is less than -200 mV,  the digital signal is 1
• When V a  – V b  has a voltage greater than +200 mV  is digital signal 0

In order to work many of these devices together you have to have a Master and Slave connection. The Master is connected to the Slaves and will call on each Slave device by its number. You can then connect this to your computer. The computer will use the RS232 chipset and convert this to the RS485 chipset with an RS232 to RS485 converter in order for the computer to understand the Slave devices. You can have 256 devices or using a repeater you can connect thousands of devices. See also the rs485 to usb driver and the usb rs232 driver.

Characteristics of the RS485

Standards

The RS232, RS423, RS422, and RS485 communication standards exhibit distinct characteristics:

In terms of differential signaling, RS232 and RS423 do not support it, while RS422 and RS485 both employ differential signaling. The maximum number of drivers is limited to one for RS232, RS423, and RS422, whereas RS485 allows for up to 32 drivers. For receivers, RS232 accommodates one, RS423 supports up to 10, and RS422 supports 10 (32 in multidrop), while RS485 can handle up to 32. Likewise see also the XR16L580 UART on here.

Modes of operation vary, with RS232 being half duplex (full duplex at 12 m), RS423 operating in half duplex, and both RS422 and RS485 utilizing half-duplex communication. Network topology differs, as RS232 is designed for point-to-point connections, RS423 for multidrop, RS422 for multidrop as well, and RS485 for a multipoint setup. The maximum communication distance, as per the standard, is 15 m for RS232 and 1200 m for RS423, RS422, and RS485. See more on the working principles of RS485 on here.

Speed

Speeds at 12 m vary, with RS232 supporting 20 kbs, RS423 at 100 kbs, RS422 at 10 Mbs, and RS485 at 35 Mbs. At a distance of 1200 m, RS232 and RS423 operate at 1 kbs, RS422 at 100 kbs, and RS485 at 100 kbs. RS232 features a slew rate of 30 V/μs, RS423 has an adjustable slew rate, while RS422 and RS485 do not specify. See also the USB Front ports not working? on here.

Receiver input resistance differs, with RS232 at 3..7 kΩ, RS423 at ≥ 4 kΩ, and RS422 at ≥ 4 kΩ, whereas RS485 has a higher requirement at ≥ 12 kΩ. Driver load impedance varies, with RS232 at 3..7 kΩ, RS423 at ≥ 450 Ω, RS422 at 100 Ω, and RS485 at 54 Ω. Receiver input sensitivity is ±3 V for RS232, ±200 mV for RS423, RS422, and RS485. Likewise see also the CP2112 USB Bridge Driver on here.

Input voltage ranges differ. With RS232 at ±15 V, RS423 at ±12 V, RS422 at ±10 V, and RS485 at –7..12 V.  Maximum driver output voltage varies. The RS232 at ±25 V, RS423 at ±6 V, RS422 at ±6 V, and RS485 at –7..12 V. Minimum driver output voltage with load shows distinctions. Such as RS232 at ±5 V, RS423 at ±3.6 V, RS422 at ±2.0 V, and RS485 at ±1.5 V

Why mix them is that the RS485 can send signals up to 1,200 meters while the RS232, that can send signals only 15 meters. See also the article on the RS232 as well as adapters for these standards. See the pl2303gt driver as well as the ft231x usb uart driver on here.