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Whats UART->USB Chip like FTDI FT232RL is Thinking in Term of Mbps Speed?

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Mechatrommer:
maybe an old statement, but... FTDI claimed to support USB2.0 full speed, ie 12Mbps = 1.5MBps, but i only can do 64KBps fastest with it, WTF?!
64KBps is USB0.5. not even close to USB1.1 Std Speed 1.5Mbps (187KBps)
whats the faster uart to usb chip out there? 480Mbps will be better, USB3 5Gbps will be the best. even the USB1.1 187KBps++ will be better than FTDI232RL!

Simon:
USB2.0 is 480 Mbps

enz:

--- Quote from: Simon on November 07, 2011, 05:26:50 pm ---USB2.0 is 480 Mbps

--- End quote ---

This is normally called High-Speed, while Full-Speed refers to 12Mbps.


--- Quote from: Mechatrommer on November 07, 2011, 04:54:47 pm ---maybe an old statement, but... FTDI claimed to support USB2.0 full speed, ie 12Mbps = 1.5MBps, but i only can do 64KBps fastest with it, WTF?!
64KBps is USB0.5. not even close to USB1.1 Std Speed 1.5Mbps (187KBps)
whats the faster uart to usb chip out there? 480Mbps will be better, USB3 5Gbps will be the best. even the USB1.1 187KBps++ will be better than FTDI232RL!


--- End quote ---

The reachable USB transfer rate heavily depends on the device you are talking to and the software you are using.
1. What is the exact setup for your transfer rate mesurement?
2. What device are you talking to
3. Are you using ths VCP (Virtual Com-Port) drivers or D2XX driver
4. If you are using the VCP driver, of course your transfer rate will belimited to the configured baudrate.

Maybe these points can give you some hints.

Best regards,
Martin

ejeffrey:
Full speed vs. low speed is mostly important because it limits the amount of bus time taken up and low-speed devices have limitations on packet length and type.  The protocol speed is limited by the operating speed on the UART side.  The fastest standard rate (from the 16550A UART family) for RS232 is 115.2 kbps.  Multiples of that up to around 920 kbps are pretty common.  The FT232R data sheet claims that it operates at up to around 3 Mbps, or 300 KB/s (each byte takes 10 bit slots counting the start and stop bits).  The actual usable baud rate will depend on your level shifter and cable (if present), and receiving device.  Also, that is the signaling rate: depending on the speed of your endpoint devices you may not be able to saturate it.

Even if you find a transceiver that supports it, very few devices can talk RS232 at much above ~ 1 Mbps or RS485 at above 10 Mbps.  If you need much higher speed, you will probably be better with a protocol designed for that purpose -- native USB being the most obvious answer.

jahonen:
Don't mix signaling speed with real speed you get using certain USB device. 480 Mbit/s is the gross bit rate, and depending on the used packets, the actual throughput might be very much less. In fact, if you send only one character per packet, then you can only send about 8000 characters per second, since USB 2.0 microframe interval is 125 ┬Ás.

If you want maximum throughput in an application level, then you have to use full custom USB device using USB endpoints directly, forget those serial UARTs. Note that operating system may also limit the actual throughput for various reasons, like you can't get the theoretical latency for the data transfer but instead it is similar to the task scheduling interval.

Regards,
Janne

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