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Observer tish
Observer
343 Views
Registered: ‎08-20-2019

How to use the PMOD USB UART module

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Hi. I am working with Zedboard. Can anyone advice me regarding how to use the PMOD USB UART module? Do I need to include the soft IP core in the block diagram? If so then where can I get the soft IP core of this module?

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Scholar u4223374
Scholar
270 Views
Registered: ‎04-26-2015

Re: How to use the PMOD USB UART module

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@tish Two very common problems with UARTs:

 

(1) Have you got the right COM port selected? This is most easily achieved by opening Device Manager and then plugging in the USB cable to the PMOD USB UART - the new device that pops up is the COM port you need to select.

(2) Have you got RX and TX the right way round? UART naming conventions are a mess, so you invariably have the question "is this RX pin data received by the FPGA (transmitted by the PC), or received by the PC (transmitted by the FPGA)?" For an initial test, I'd be tempted to just drive both the TX and RX pins from the FPGA - which is horrible electronic design practice, but I've never actually managed to do any damage when I've done this by accident.

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Xilinx Employee
Xilinx Employee
321 Views
Registered: ‎07-11-2019

Re: How to use the PMOD USB UART module

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Hello @tish 

I have attached a tutorial on how to get started with the PMOD IP Cores as well as the datasheet for the USB UART module for reference, so that everything is in one place. Lastly, I have attached a link to another forum thread very similar to yours, and I believe they have information on how to get started that you might find useful. Good luck on your project! 

Attachements

Datasheet: https://reference.digilentinc.com/_media/reference/pmod/pmodusbuart/pmodusbuart_rm.pdf

Tutorial/Example Project: https://reference.digilentinc.com/learn/programmable-logic/tutorials/pmod-ips/start

Forum: https://forums.xilinx.com/t5/Spartan-Family-FPGAs-Archived/Sending-serial-data-via-PmodUSB-UART-component/td-p/201167

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Observer tish
Observer
298 Views
Registered: ‎08-20-2019

Re: How to use the PMOD USB UART module

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Thank you for replying. I have checked the datasheet. Do I have to set the rts and cts signals explicitly? Or I can ignore those signals?

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Scholar u4223374
Scholar
284 Views
Registered: ‎04-26-2015

Re: How to use the PMOD USB UART module

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Almost every UART just ignores the hardware flow control (RTS, CTS, etc). They only use RX and TX, and if flow control is required then that's done in software (eg. XON/XOFF characters). When sending to a modern PC (or any PC built after about 1987, when the 16550A UART was introduced) there's no need to do any flow control (because a PC can easily cope with RS232 data rates), and most of the time an FPGA also doesn't need it (because you can process the required data in far less time than it takes to actually receive the data).

Observer tish
Observer
279 Views
Registered: ‎08-20-2019

Re: How to use the PMOD USB UART module

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@u4223374 Thank you. Then what is the problem with my system I dont get it. I am getting the Uart output from the pmod female pins but when I am attaching the module to the same pins nothing is being printed on the terminal emulator. I have checked and set the same baud rate. Please can you help me? 

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Scholar u4223374
Scholar
271 Views
Registered: ‎04-26-2015

Re: How to use the PMOD USB UART module

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@tish Two very common problems with UARTs:

 

(1) Have you got the right COM port selected? This is most easily achieved by opening Device Manager and then plugging in the USB cable to the PMOD USB UART - the new device that pops up is the COM port you need to select.

(2) Have you got RX and TX the right way round? UART naming conventions are a mess, so you invariably have the question "is this RX pin data received by the FPGA (transmitted by the PC), or received by the PC (transmitted by the FPGA)?" For an initial test, I'd be tempted to just drive both the TX and RX pins from the FPGA - which is horrible electronic design practice, but I've never actually managed to do any damage when I've done this by accident.

Observer tish
Observer
214 Views
Registered: ‎08-20-2019

Re: How to use the PMOD USB UART module

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Yup actually that happened @u4223374 . The Rx and Tx pins were messed up. Thanks. 

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Scholar u4223374
Scholar
203 Views
Registered: ‎04-26-2015

Re: How to use the PMOD USB UART module

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Hah, get used to it - it'll keep happening. SPI and I2C are much, much nicer interfaces (SPI because it uses sensible naming, I2C because everything is bidirectional anyway).

 

On a custom PCB, you can put a pair of SMT 1K resistors next to each other so the pads form a square, with opposite corners going to the same chip (ie north and south pads go to the FPGA, west and east go to the USB-UART). That way, if you mess up the connections, (a) the chips are protected because there's a 1K resistor between them, and (b) if you rotate both resistors by 90 degrees then that neatly fixes the connections. Of course, on an FPGA there's no need to do this because you can modify the pinout in software - but a 1K resistor is still not a bad idea.

 

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