2.rs-485 interface allows as many as 128 transceivers to be connected on the bus, and has multi-station capability, so users can easily establish a device network by using a single rs-485 interface.
3. The signal level of 3.rs232 interface is high, which is easy to damage the chip of interface circuit, and because it is incompatible with ttl level, it is necessary to use a level conversion circuit to connect with ttl circuit.
4. The transmission rate is low and the baud rate is 20kbps in asynchronous transmission; Therefore, on the development board of South Laoshu 5 1cpld, the baud rate of the integrated program can only be 19200, which is also the reason.
Extended data:
In the past, the communication between PC and intelligent devices mostly depended on RS232, RS485 and Ethernet, mainly depending on the interface specifications of the devices. However, RS232 and RS485 can only represent the physical medium layer and link layer of communication. If you want to realize two-way data access, you must write your own communication application programs, but most of these programs can't meet the ISO/OSI specification, and can only achieve a single function, which is suitable for a single device type, and the programs are not universal.
In a device network composed of RS232 or RS485 devices, if the number of devices exceeds two, RS485 must be used as the communication medium. The information exchange between devices in RS485 network can only be realized through the transmission of "master" devices. The master device is usually a PC, but only one master device is allowed in this device network, and the rest are slave devices.