Which USB-RS232 adapter to get?
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Yes, a RS232 to USB converter does have a full-blown UART circuit built-in. As any standard UART, it does have Rx, Tx, and flow control pins. As any UART, it must be properly configured to be able to communicate with the "partner" at the other end of UART link.
To do so, the UART circuit is "bridged" to USB interface. The USB interface has the CDC class descriptor (Communication Device Class), and the USB host driver maps this USB device into a virtual COMnn port with nearest available number, so PC applications can use it as an usual COM port.
The bridge is fairly simple. To read the UART data, the USB COM port driver is constantly asking the USB device for data (since it has no other means to know when the UART will receive its data and will be ready to give them to host). When there is no data, the bridge responds with NAK. When data is there, the USB side returns the piece of data.
When the host wants to send a UART data, it issues an OUT packet with 1 byte of data. The bridge receives the serial byte into a parallel buffer (at USB speed), and then stuffs the received parallel byte into the parallel side of UART for transmitting it at UART's speed.
Before communicating over UART, the USB side must configure the UART for proper baud rate, stop signal length, and use of flow control, as in case of usual UART in a PC. This is virtually transparent to application terminals, and the terminals use the usual interface to set these parameters up.
Yes, many such RS-232 to USB adapters have a USB-to-UART chip. Common ones are:
- Cypress CY7C65213
- Microchip MCP2200
- FTDI FT232R
Hi,
I'm not sure where to post this question, since I haven't been able to find a subreddit about this specific topic, so I hope it's alright to post it here, since I've seen some similar thread.
I would like to buy a new USB to RS232 adapter, since the ones I've tried so far, which all have Prolific chips, doesn't work as expected for me. I'll mostly be using the adapter at 9600 baud, but will occasionally be using it at 57600 baud for firmware updates to a unit, which the program does by looking for a 16550 port, and going to 57600 baud if it finds one.
I've looked at the StarTech ICUSB2321F and the Eaton Tripp Lite Keyspan, which both look good, but I'm unsure which one is best?
My main problem with the adapters using Prolific chips was that it often seemed to give much lower transfer speeds than what is possible with 9600 and 57600 baud. I've read a lot of good things about the Keyspan, and I like that the USB cable is apparently detachable. It also appears to have the fastest transfer speeds, but I've seen some claim that it doesn't always works with older Dos programs that tries to detect 16550 ports, which is what I'll be using. Other than Dos, I'll mainly be using it with Windows 7 and Windows 10.
Has anyone here tried or compared both products? What should I do?
Thank you.