Self-made Siemens PLC programming cable
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It is possible to make one’s own programming cable for Siemens PLCs. The original Siemens S7200 PLC programming cables are quite expensive; therefore, when no original cables are available, it is possible to create them oneself. The following are the steps involved, for reference only. I have been using this method for many years, and it works fairly well. First, if the computer doesn’t have an RS232 port, it is necessary to purchase a USB-to-RS232 cable. Second, buy an RS232-to-RS485 adapter (the price is around 40 yuan). It is possible to make such an adapter oneself, but those homemade ones are not as good as commercially available ones. To ensure reliability, it’s better to buy one. Third, prepare male and female 9-pin connectors, as well as several meters of network cable. Fourth, connect RS485’s D+ (A+) to port 3 of the PLC using the network cable, connect RS485’s D- (B-) to port 8 of the PLC, and connect RS485’s GND to port 5 of the PLC. Fifth, make sure the connections are correct; never connect port 7 of the PLC to the RS485 interface, as port 7 is used for the 24V power supply. Sixth, open the programming software and download (or upload) the necessary files.
I have only worked on cables that connect the TD200 to the PLC; I haven’t worked on this type of cable yet. It’s a special cable from Siemens, and if I had seen it earlier, I would have followed your method. Have you used it before?
Replying to floor 2: I’ve been using it for many years now; it works pretty well. The only issue is that the RS232 to RS485 converter isn’t as good as the original one, as the original version comes with optocoupler isolation.
If you are learning in the laboratory and can only use self-made cables, it is highly recommended to purchase original cables for debugging, as there have been many cases where problems with the programming cables led to failures in establishing connections during debugging. Don’t lose the big picture for small gains. Which is more significant, the loss caused by a one-day delay in production or a single cable?
They are available in Zhongguancun, Beijing; they cost a few dozen yuan each. There is no isolation mechanism, and it’s absolutely necessary not to plug or unplug them while they are powered on. Inside, there are just a few resistors, but they work quite well