Ehhhh, maybe not such a good "Friend".
Never used that chip, but looking at the datasheet, it seems that it's mostly a "HUB".
It does accept rs232, keyboards, mice and stuff.
But the conversion is to USB, not RS232.
I don't see any way to read the keyboard with an MCU.
Could be I just haven't read far enough.
If you want FTDI, then I think the ...
Vinculum Embedded USB Host Controller
http://www.ftdichip.com/FTProducts.htm#Vinculum
might get you closer.
DT
Darrel,
You're right (again). Vinculum is the way to go, and that chip I mentioned is a hub with 7 downstream and one upstream.... it may work, but not experimenting any more if I can avoid it. I bought what was available at Akihabara today - a USBN9604, which is a node controller from National Semicon. Can't wait to get out of this meeting and back home to put things together.
If I may ask another question...
1) I understand that coding away to filter all the stuff that would come in on a comparator would be an arduous task, but why is speed an issue? People can only type so fast. Or, would the comparator require a couple cycles each time doing it's thing? I know my code would require a couple of cycles to filter the signal as well. Gave up on that route for this particular endeavor, but still fishing around for information just because I want to know more about that function on MCU.
Last edited by kirtcathey; - 9th January 2009 at 08:40.
Well, let's say that an 18F is running at 48Mhz. (the fastest 8-bit PIC)Originally Posted by kirtcathey
Divide that by 4, and the CPU core will execute 12 million instructions per second.
Full-speed USB is 12 million bits per second. So at best, you could only execute 1 instruction of your program per incoming BIT of data.
Now, considering it takes 4 instructions to copy the state of a pin to a BIT variable. It's easy to see that it just can't be done with software.
Plus there is a LOT of overhead communication with USB. Even if nobody was typing on the keyboard, there's still a ton of data being passed back and forth. The computer is constantly asking the device ... "Are you there", and the device says ... "Yup, I'm here", over and over and ...
When it gets unplugged and the computer doesn't get an "I'm here" anymore, it disconnects the device driver and you hear the ding-dong.
So basically, USB interfaces MUST be done with hardware.
hth,
DT
Technically, the fastest 8-bit PICs are the PIC18FxxKxx series that are rated at 64Mhz. But you are absolutely correct about USB stuff being done in hardware.
I stand corrected!
I will now have her give me 40 lashes for the error.
WooHoo!
DT
Thank you.... soldering the USB controller chip onto a daughter board right now. When I get the whole rig breadboarded and working, will update my schematic and post it here.
Again, thank you for all the direction.
How about a different approach:
Take a PS/2 keyboard and a PS/2-USB adaptor and tap the data on the PS/2 side.
There are a lot of keyboard interfacing examples out there...
Regards,
Ingo
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