编程电缆说明(国外英文资料).docVIP

编程电缆说明(国外英文资料) There are many posts on the PC/PPI cable in the forum. Let me talk about the PC/PPI cable. Because I have not done similar anatomy or cable, only to talk to speculate that errors and inappropriate, please dont hesitate to point out mistakes. And I havent seen the new USB and the latest 6ES7 901-3CB30-0XA0 cable. Im not familiar with the two cables. 1, why use the PC/PPI interface? Because the S7200CPU uses RS485, and the COM port of the PC machine uses RS232, the electrical specifications of the two are not compatible, and need to match with the intermediate circuit. PC/PPI is actually a RS485/RS232 matching cable. 2, RS485 uses two A/B points difference line communication, relative level A and B with two lines to represent 0 and 1, the same time only by a bus driver and other devices on the bus at this time are in the receiving state; RS232 RXD and TXD line interface independent, can also send and receive communications at the same time, RS232 is designed to separate communication between two devices, connection does not support more than two devices, so it can be accessed at any time, no communication collision. 3, the RS485 bus device and when it can drive the bus, is determined by the communication protocol. Neither the RS485 nor the RS232 has any extra wires to tell when the matching cable in the middle can drive the RS485 bus, and the matching cable doesnt know the exact protocol. According to the requirement of RS232 cable, unilateral send to decide whether you need to drive the RS485 bus line: when the TXD sends data pulse, matching cable immediately by the receiving state to send state, RS485 bus drivers, when the data on the TXD pulse disappeared, then turned into a cable state, allowing the other devices on the RS485 bus bus driver. 4, why set baud rate and data bit length? There is one from the PC/PPI specification: Direction, change, delay:, RS - 232, stop, bit, edge, received, to, RS - 485, transmission, disabled 1.4, character, times, m