USB keyboard decoder

Question

Hi, i have a project where i need to interface Artix7 FPGA, with usb keyboard, what is the best module or component to do this?

michaelkellett · Accepted Answer

I don't see why not, PS/2 interface uses open collector drivers with the pull ups normally to 5V. If there are no pull ups in the keyboard and you don't want to talk back to the keyboard, you might be able to pull up to only 3.3V. It's still worth having something between the FPGA and the keyboard to give it some protection, the keyboard will need 5V power. MK

michaelkellett · Answer

I think the best quick and dirty way to do it is with something like this: https://www.hobbytronics.co.uk/usb-host-keyboard There are several such devices around, best look somewhere local to you, or maybe Amazon for one in stock and cheap. Then it will be really easy to add a UART style interface to your FPGA. Or you could try one of the modules from FTDI that uses theri Vinculum device. https://www.ftdichip.com/Products/ICs/VNC2.htm MK

michaelkellett · Answer

You need to tell us a lot more about the project. Do you want to do this once, or for production. Do you care about cost. Is you FPGA on a board or will you be designing a board. Is this a task you have been set for study or do you just need the quickest way of getting keyboard data into the FPGA. Ar you running a soft processor on the FPGA or must the keyboard talk directly to RTL ? Do you mean a music keyboard or a computer keyboard ? etc etc. The answers will be different for every application.

michaelkellett · Answer

I had a play with the idea - there is a snag - of course PS2 keyboards work the way they are described and if you connect one to power with the required 2 pull up resistors it works just the way you expect. The cheap little USB Keyboard to PS2 motherboard adaptors don't contain any works (tested three different ones) - just 4 straight through connections . The keyboard has to know how to do PS2, I tried an HP USB keyboard and a Logitech K200 keyboard with the PS adapters and neither would work It's hard to find out, but the rumour on the web is that modern USB keyboards don't have any support for PS2. The good news is that you can buy a new PS2 type keyboard from Amazon for less than the Hobbytronics USB to UART converter - I suggest you consider that. But do take a look at the PS2 keyboard protocol - it's a bit of pain to work with. MK

johnbeetem · Answer

This may be too late to be useful, but here's what I'd look into. Basically, you need to be a USB host to talk to a USB device like a keyboard. USB hosts are pretty complex, which is why some people have suggested running Linux. Personally, I think that's overkill. I would recommend checking into the Maxim MAX3421E "USB Peripheral/Host Controller with SPI Interface". According to the description, this IC can be used as a USB peripheral or USB host, and should be a whole lot less work than implementing a USB host controller in an FPGA. Another possibility is a Microchip SAM D21, which is a small 32-bit microcontroller with a USB host/device interface. This would require a lot of software, but that may already be available. You should be able to find a breakout/development board for either of those chips. I have not used either of those products myself.

USB keyboard decoder

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