On 2010-07-29 14:24, ivp wrote:
>>> I suspect the keyboard is seeing the characters you are sending
>>> as commands to the keyboard, but as it doesn't know what to do
>>> with them it goes into dumb mode
>
> Alan,
>
> I'll double-check all signals when I'm at that PC tomorrow. There
> is a protocol for the PC to request the keyboard accept data
>
>> From the specs -
>
> "If the keyboard is not sending or if the system elects to override the
> keyboard's output, the system forces the keyboard clock line to low
> level for more than 60 microseconds while preparing to send data.
> When the system is ready to send the start bit (the data line will be
> low), it allows the clock line to go to high level"
>
> Now, re-reading that, possibly I'm looking at the wrong end of the
> PIC's data packet. I do send the clock line low for>  60us, and that's
> at the end of the transmission, after the Stop bit. However, the 4066
> should be isolating the keyboard from that. But it's worth checking,
> maybe there's leakage. I'm wondering why my keyboard (the waveform
> of which I copied) has that 357us low on the clock line after the Stop
> bit. I don't see it in the specifications. Perhaps reducing it to a nomin=
al
> bit width will fix the problem, without needing the 4066
>
>> Barcode readers designed to be used between a PC keyboard
>> and a PC, uses a "Wedge". Now, I do not think that thing
>> simply hard-wires the in and out connectors as in this case.
>> I'm pretty certain that it contains some electronics to isolate
>> interfaces
>
> Jan-Erik,
>
> If so, those electronics would have to allow the bi-directionality of
> the lines
>

Right, the "wedge" has to monitor the wedge-PC line to see if the
PC's tried to send. And if so, relay that over to the keyboard side.
If I understand correctly. Or simply connect the PC and kayboard
directly (if the PC wants to send). Maybe that can be built using
discrete electronics also, I havn't thought about it. I did some
Googling to try to find some exemple schematics on a "wedge", but
only come up with different text-based descriptions. All saying
that a "wedge" is what allows two sources (the keybaord and something
else, often a barcode reader) to communicate with a PC...




> Joe
>
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