Re: PIC, Keyboard, and USART


"Jan Wagner" <nospam@xxxxxxxxxx> wrote in message
news:e05sfv$2u0$1@xxxxxxxxxxxxxxxxxxxxx
Abstract Dissonance wrote:
I'm going to try to program a simple keyboard translator using the
PIC2455 which has a built in EUSART. At this point I just want to get
the keyboard codes into the pic and I just want to run this by you guys
to make sure I'm on the right track.

1. Setup hardware. Basicaly just have to connect the Data and Clock lines
to the EUSART pins on the pic
2. Enable the USART on the pic for Asynchronous mode and enable auto baud
rate dection(to make it easy).
3. Read the RCREG in the interrupt and do whatever with it(like make an
LED blink on certain codes).

Is that basicaly all I have to do? Do I need to use pullups or anything
when connecting the lines or even use transistors to source/sink more
current?

(I'm running the keyboard off a 5V supply that can source up to .5mA or
so)

Apart from the "writing bugs" others already commented on, doing this with
UART could be a real nightmare. Ok, 9600 baud and 8 databit, 1 odd parity,
1 start and 1 stop bit, and separate clock input, it is basically easy (if
your microcontroller supports that many bits!! 11 of them). But then there
is also the bidirectional communication needed especially if you want to
configure the keyboard to something sensible by sending commands to it.
Basically you'd have to switch off the UART and put the pins into output
mode for the handshakes etc, then switch back to UART again to receive or
transmit. For both receive /and/ transmit, you'd have to use the clock
provided by the keyboard, i.e. synchronous UART. It's a real mess.


yeah... after looking at slave mode I saw this. Difference between master
and slave is who supplies the clock.

I was thinking that all I would have to do is switch between master and
slave mode for tranmission and reception. Not sure if this would work
though or not... I'd still have to setup the clock speed properly for
tranmission but I figure that it shouldn't be to hard to do cause they are
two disjoint parts. The main problem is when worrying about collisions.

You can find some valuable background info at
http://www.beyondlogic.org/keyboard/keybrd.htm#1


Yeah, I'm still trying to read up on all this stuff. Its a good site but
trying to make some sense of the data*** for the pic. It gives different
methods to do the same thing and I'm confused on which is right.

If you only want to receive, and your uC does support full 11 bits UART
("Enhanced USART" sounds like it might, but then maybe that's just
marketing bull...) then this should be very easy to do.


Well, I'm not sure. It says 9-bits but not sure if that includes the start
and stop bit ;/

Just add the pull-up resistors, data line to UART RX, clock input not
strictly necessary - until you want to transmit.


? Is that for asynch mode? I'd need to use the clock in slave mode for the
getting data? (since I don't know its data rate). I could use asynch mode
and auto detect the clock but I'm not sure how reliable this is ;/ and I
think there has to be a calibration test or something and I have no idea how
to get that done.

regards,
- Jan

Thanks,
Jon


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