1, it depends on what you are doing, just experiment, use a cheaper chip, 75176. If you are doing a project, you need to use a reliable quality, the best is 75LBC184, internal ESD protection circuit, more safe to use. The following figure is its information introduction.
2, max485 Ah, this is very common. And the max485 is relatively cheap, and we all use it on our boards.
3, so it is better to choose the popular two-bus way, like powerbus bus, mbus bus, generally voltage, current return, the communication mechanism is different, determines the anti-interference ability is too strong, and can even be with 220 mains or even 380 power power common slot. Several chip models are recommended, powerbus pb620.
4, with the serial port expansion chip, WK2204 or WK2168, through SPI/I2C/UART/ 8-bit bus to expand 4 serial ports, the chip supports RS485 automatic transceiver, through the extended UART connected to RS232 and RS485 level conversion chip can be. WK2204 and WK2168 both have RS485 automatic transceiver function, which is very convenient.
RS-485 is a physical interface, in short, that is, hardware.
In industrial control occasions, RS485 usually refers to the RS485 interface, which belongs to the hardware equipment. RS485 bus is widely used because of its simple interface, convenient networking and long transmission distance.
RS485 is a definition of a balanced digital multipoint systemA standard for the electrical characteristics of drivers and receivers, as defined by the Telecommunications Industry Association and the Electronic Industry Alliance. Digital communication networks using this standard can effectively transmit signals over long distances and in environments with large electronic noise.
RS485 is a standard that defines the electrical characteristics of drivers and receivers in balanced digital multipoint systems, as defined by the Telecommunications Industry Association and the Electronic Industry Alliance. The box area in the following figure shows the RS485 port. RS-485 is also known as TIA-485-A, ANSI/TIA/EIA-485 or TIA/EIA-485.
protocol refers to the RS-485 protocol, which is the standard for serial communication. Typical serial communication standards are RS232 and RS485, which define voltage and impedance, but do not define the software protocol.
RS485 is a communication bus, consisting of two communication lines, and transmits differential signals. RTU Is not MODBUS-RTU? This is a communication protocol that runs on RS485. It's similar to running TCP/IP on an 8-core cable.
RS-485 interface allows up to 128 transceivers to be connected on the bus. With multi-station capability, users can easily set up device networks using a single RS-485 interface. The RS-485 interface is the preferred serial interface because of its good anti-noise interference, long transmission distance and multi-station capability.
You can also use a circuit to simply control the sending and receiving end.When the data is sent, the data is sent to the data input end DI of the Max485 chip, and the positive and negative logic levels of the data are driven to the A line and the B line respectively by the sending enable end RE and DE.
2, because MAX485 works in the half-duplex state, so only one pin of the single chip computer can be used to control the two pins; Terminal A and terminal B are the receiving and transmitting differential signal terminals respectively. When the level of pin A is higher than that of pin B, the data sent is 1. When the level of A is lower than that of B, the data sent is 0.
3, transceiver principle circuit --Automatic sending and receiving: that is, without the single-chip pin DR, when the data comes in, the data will be automatically sent to the single-chip through RXD, and when the data needs to be sent, it will be automatically sent out through TXD.