1. The PPI protocol is a communication protocol developed specifically for the S7-200. The communication port (Port0, Port1) of the S7-200 CPU supports the PPI communication protocol, and some communication modules of the S7-200 also support the PPI protocol. Micro/WIN programming communication with the CPU also passes the PPI protocol. PC Cable:MINI DIN,D-SUB,SCSI.The display connecting line includes the data cable connecting the host computer and the display screen, and the power cable connecting the power supply.
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The PPI network communication of the S7-200 CPU is based on the hardware of the RS-485 network, so its connection properties and required network hardware devices are consistent with other RS-485 networks.
PPI network communication between S7-200 CPUs requires only two simple instructions, which are Network Read (NetR) and Network Write (NetW) instructions.
The PPI protocol is a proprietary protocol of Siemens. The specific details are not disclosed and are generally used for communication between Siemens devices.
2, free mouth:
The communication port of the S7-200CPU can be set to free port mode. After selecting the free port mode, the user program can completely control the operation of the communication port, and the communication protocol is completely controlled by the user program.
The communication port on the S7-200 CPU is electrically a standard RS-485 half-duplex serial communication port. The format of this serial character communication can include:
One start bit
7 or 8 characters (data bytes)
An odd/even parity bit, or no parity bit, a stop bit free port communication speed baud rate can be set to 1200, 2400, 4800, 9600, 19200, 38400, 57600 or 112500.
Any serial communication device that conforms to these formats can theoretically communicate with the S7-200 CPU.
The free port mode can be applied flexibly. Micro/WIN's two instruction libraries (USS and ModbusRTU) are implemented using free port mode programming.
In order to reduce the mutual crosstalk and external interference between loops, the cable adopts shielding structure. According to different occasions, the shielding requirements of cables are as follows: the combined shielding of twisted pair, the total shielding of cable composed of twisted pair, and the total shielding after the combined shielding of twisted pair.
Shielding materials include round copper wire, copper strip and aluminum / plastic composite belt. Shielding pair and shielding pair have good insulation performance. If there is potential difference between shielding pair and shielding pair, the transmission quality of signal will not be affected.