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'PC-AT keyboard add-on #2'
|After thinking a bit more on my previous posting:
simple circuit that can attach to an existing keyboard-PC connection in order to add extra key codes into the PC on switch operations.)
I got a response that indicated a problem with interfering with the existing connection and that the existing codes should be transferred intact etc. Got me thinking:
Is it possible to make the unit to add extra keycodes to the PC the following way:
1. Connect a 2-pole relay in series with the data and clock signals from the keyboard
2. Connect the PIC to the data and clock on the PC side of the relay
3. When a switch is detected on the PIC do the following sequence:
- Wait until there is no activity on the data/clock lines (both high)
- Activate the relay to disconnect the keyboard
- Start sending the key code to the PC corresponding to the PIC input
- Check PC response
- Release relay
PS: This list seems rather quiet nowadays, when I last subscribed there was a mass of postings all the time. What happened?
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Bo Berglund wrote:
> - Wait until there is no activity on the data/clock lines (both high)
> - Activate the relay to disconnect the keyboard
> - Start sending the key code to the PC corresponding to the PIC input
> - Check PC response
> - Release relay
> Any comments?
Yes, 1} You don't use relays, you use gates
2} This doesn't handle keypresses while the alternative
"keyboard" source is sending.
There are two ways of handling this. Either "busy" out the keyboard
by pulling the relevant line low whilst sending from the alternative
source, or set up a repeater function, with buffering (probably only one
keycode) between keyboard and PC.
I can't speak for which of these methods keyboard wedges *actually*
use these days.
> PS: This list seems rather quiet nowadays, when I last subscribed
> there was a mass of postings all the time. What happened?
You should be receiving 70 mails daily during the week and 20 daily on
the weekend. You should receive this mailing twice, one via the list.
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