The method for determining whether the serial port is 232 or 485 is as follows:
First, look at the device connection object, the general PC often uses RS232, PLC commonly used RS485, of course, similar to S5 interface and RS422 way.
Initially look at the number of linked equipment, multiple equipment is generally RS485\/422, a single may be RS2323, see if there is no terminal resistance, which is the symbol of RS485.
Secondly, you need to use an oscilloscope to measure before you can confirm the port type
1, RS232, 2,3 pin to 5 pin communication when the measurement of positive and negative 15V voltage.
2, RS485, commonly used 2, 3 pins, 5 pins is ground, differential voltage -7 ~ 12V3, RS422, usually 1,6 pins is 9V power supply, usually use 2, 3, 4, 5 pins, differential voltage plus or minus 10V, through different characteristics to distinguish:
1, 485 interface: logic \"1\" to the voltage difference between the two lines is (2-6) V; The logical \"0\" is represented by the voltage difference between the two lines as - (2-6) V.
2, 232 interface: Because the external power supply mode is not used, you must take power from the RS-232 interface line to supply power to internal components.
Second, by different levels to distinguish:
1, 485 interface: the interface signal level is lower than RS-232-C, it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, which can be easily connected with the TTL circuit.
2, 232 interface: RS-232 communication interface adopts level mode transmission, suitable for point-to-point communication, without special transceiver enable control.
Third, distinguish by different power consumption:
1, 485 interface: The combination of balanced driver and differential receiver, anti-common-mode interference ability is enhanced, that is, anti-noise interference is good.
2, 232 interface: The converter power supply from the RS-232 signal line, its input power is limited, so in this design will be as far as possible to use 3V power supply of low-power devices.