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ps2 keyboard port maximum data rate?

Posted on 2011-09-13
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Last Modified: 2012-05-12
I'm programming a hardware keyboard wedge and wondering about the data rate. What maximum data rate might I expect from a desktop's ps2 keyboard port?
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Question by:FuturesTrader
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5 Comments
 
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Expert Comment

by:inetman
ID: 36533412
keystrokes per minute is the number your looking for. So 255 should be a good size, as I do not know of anyone that types that many keys per second. normal people type 30-60 wpm. I can do slightly better.. so if you set your buffer to that size it should work great.
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Expert Comment

by:Dave Baldwin
ID: 36533424
This page looks like it has the info: http://www.computer-engineering.org/ps2protocol/  Note the variable clock rate, 10-16.7KHz.
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Author Comment

by:FuturesTrader
ID: 36533515
would a safe assumption be that a 10khz clock rate translates to a single character worst case delay of ~100 microsecs?
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Author Comment

by:FuturesTrader
ID: 36533522
hmmm... actually a worst case delay would occur when the character arrived at the port at exactly the worst time in the clock cycle.. or if the clock is generated in the keyboard the character would be sent at that time. Either way would the worst case single character delay be about 200microsecs?
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Accepted Solution

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Dave Baldwin earned 500 total points
ID: 36533576
No, that interface is much slower than that.  10KHz data rate at 11 bits per character is only 900 bytes per second.  But this is a bidirectional interface and the controller in the computer can take over and send status bytes back to the keyboard.  Or worse yet, interrupt the current transmission and require it to be resent.  Since PS2 was a keyboard or mouse interface, speed was not considered to be an issue.
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