Reading a PS/2 mouse

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I have some source codes that should be able to read a mouse through
the PS/2 port on the Xilinx fpga board; it sends $F4 to the mouse and
then wait for data from the mouse.  However, I probed the ps/2 port of
the mouse and found that the mouse is not sending signals (clk & data),
both signals constantly stay at around 4V (Vcc = 5V).  (I attach the
mouse to the PC & probe the same port, and there are signals
responding.)  What would be the possiblities of such failure?

Re: Reading a PS/2 mouse
Seems like  there is problem initializing the mouse.
The host pulls the clk down to start initializing; however, the mouse
clock doesn't start after the host releases the clk.

Re: Reading a PS/2 mouse
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Just a few quick questions -
* What FPGA?  It is 5V compatible?
* Are you driving the line to 'Z' (tri-state), or to a '1'?

The fact that the line is about 4V smells bad - could you have contention?


Re: Reading a PS/2 mouse
Thanks for your reply, Jeremy!

I was using Xilinx Spartan 2E 200 on Digilent D2Sb with DIO4 extension
board.  I'm driving the line to 'Z' not to '1'.  However, after probing
the PS/2 port (6 pin mini-DIN)on the board without attaching a mouse, I
found that the data and clk stay at '0' always (according to the
schematic from Digilent, there is no pull up circuit on both PS/2 data
and clk lines).  When I probe the corresponding fpga pins, they work as
I programmed (logic 1 = 3.3V, logic 0 ~0V).  Seems like the fpga
couldn't take control of the port!

I will try to use another board (XESS XSA3S1000 with Xstend V3.0) and
see if this happens.

Re: Reading a PS/2 mouse
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!?  Sounds a touch odd.  If the pins are connected to the PS/2 port,
then you would expect the port and the pins to be the same.  If you take
the PS/2 port as the reference, then it would perhaps be a case of
enabling the pullup resistors in the IOB (xc_pullup attribute for
synplify - the xilinx attribute is PULLUP (from memory))).  This
wouldn't explain your original problem though.

Guess you need to find out why the pins and the port don't match :)  The
other point of course, is that you state that the protocol uses 5V - but
you're driving 3.3V?

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re:Reading a PS/2 mouse
A stupid question but... If you are using a daughterboard and are onl
reading 0V, are you sure that

- The daughterboard is correctly connecte

- You use the proper IO pins on FPG

Re: Reading a PS/2 mouse
Yes I did, those are the only IO pins that I can use and it is
correctly connected.

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