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I need to generate a 10 MBit RS485 (UART) data stream with an USB device. Until now, I thought that the FT2232H perfectly suit but as far as I understand, the FT2232H can only generate 12 MBit or 8 Mbit as the subdividers are limited for the main divider 0 and 1. The USB device should enumerate at the PC as serial interface which supports a baudrate of 10 Mbit.

So any idea which chip is suited for the specific task?

Thanks.

steffenmauch
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  • Full-speed USB requires a 48 MHz clock because its bit rate is 12 Mbps, so most USB devices you find will have a clock speed of 48 MHz, 72 MHz, or some divisor of those. So it's actually pretty unlikely that you will find a device that gives you a 10 MHz serial baud rate. Why do you need that? You might need to have a USB connection that uses a more standard baud rate like 115.2 kHz, and then feed it into a custom microcontroller board clocked at some multiple of 10 MHz in order to convert the signal. – David Grayson Sep 29 '16 at 18:01
  • You can (theoretically) get 100Mbits (or even 1G) if you use USB to ethernet. Just saying. RS485 at 10Mbit only goes 50 feet, 100baseT goes 100m. – DisappointedByUnaccountableMod Sep 29 '16 at 18:20
  • Thanks for the suggestions; I need the 10 Mbit serial datastream to test an external device. Therefore I can't change the baudrate. What uC would be suited? The STM32 only supports 10.5 MBit ... – steffenmauch Sep 29 '16 at 21:25

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Ok, I finally implemented a suitable solution. Set the baud rate to 12 MBit and use 2 Stop and 1 parity bit. Implement a 12 MBit RS422 receiver in a CPLD or FPGA and connect it directly with the FT2232H. The CPLD/FGPA removes one stop bit and the parity bit.

Output the received data in the CPLD/FPGA with an regular 8N1 10 MBit RS422 sender. In total, this must be done twice but with 12 and 10 MBit being switched.

Works like a charm and the CPLD can even be a QFN32 Lattice iCE40 CPLD.

steffenmauch
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