USB to COM, how does the RS-232 interperate data?
https://stackoverflow.com/questions/7515915
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RussianQuestion
If I had a RFID reader that sends a bunch of keystrokes through USB like a HID, how would the COM port interperate that if I used a USB to COM converter? What would the COM port see?
Solution
You should see the "keystrokes" from the rfid device.
At the link level, the converter should take care of speed mismatch issues. It does this via an internal buffer or by throttling the sender.
But the HID protocol is more than simple keystrokes. So either the additional information will be suppressed by the USB-COM converter or it won't be. This issue may also be converter-dependent.
In this sort of HW mashup, the best thing is to try it and see. (And then write a blog post about what you discovered.)
What is your overall goal? What sw are you trying to connect the RFID reader to?
Added I agree with @Turbo J's point: most every USB-COM converter acts as a USB device. As such, if you connect them to another USB device, nothing will happen since you're using them "the wrong way around."
You'll need to find a USB/Host to COM converter. The usual name for such things is "computer" -- a used laptop may be your best bet if you want to continue down this road.
OTHER TIPS
On USB, a device can only talk to the host.
The RFID reader is a device. The USB->COM converter is a device. They cannot talk to each other wihout a host.
Conclusion: If you want the RFID data going out of the COM port, write a program which does that - by reading the HID data from RFID device and writing to the USB COM port.
Probably nothing. COM ports are usually very low speed things (you can usually tweak them up to about 115kbps. USB ports are (by comparison) incredibly high speed ports. I think the lowest speed USB is like 1.5mbps.
The more important question is how you are going to make the physical conversion. You have an RFID reader that has a usb plug on it. Are you going to chop this off and solder a db9 connector on the end, which you are then going to plug into an USB to COM adapter and try to read serial data off the com port? You are adding in one more step into it that you don't need to (you're taking up an usb port anyway).
