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???
07/13/06 06:12
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 		 #120145 - D+ and D- is not differential at the begining
Responding to: ???'s previous message
Hi Craig,

Initially the D+ and D- is not differential. They have a 15k resistor connecting to the ground. I tried to connect a PS2 keyboard to the USB port and I found the voltage at D+ and D- is arround 3.7V. I think the reason is that normal keyboard will have a pull up of 4.7k. This pull up and the 15k resistor form a potential divider which divide the 5V into 3.7V.

List of 28 messages in thread
TopicAuthorDate
Auto-detecting USB and PS2            01/01/70 00:00      
   Power            01/01/70 00:00      
      Power didn't tell            01/01/70 00:00      
         So it's on the same connector ?            01/01/70 00:00      
            I will try            01/01/70 00:00      
            Too long to detect            01/01/70 00:00      
            nope            01/01/70 00:00      
         Mechanical solution            01/01/70 00:00      
            Cable is fixed            01/01/70 00:00      
               How to do it.            01/01/70 00:00      
                  USB Expert            01/01/70 00:00      
            Why not ...            01/01/70 00:00      
         why not put the 'intelligence' into the adapter            01/01/70 00:00      
            Cost/complexity issues            01/01/70 00:00      
               then go the other way            01/01/70 00:00      
                  Still need hardware            01/01/70 00:00      
                     you\'ll need that anyhow, how else?            01/01/70 00:00      
            Agree with Chris            01/01/70 00:00      
               Which is why I suggested Cypress            01/01/70 00:00      
      float to ascii            01/01/70 00:00      
         Start a New Thread and ask again            01/01/70 00:00      
         start a new thread!            01/01/70 00:00      
   Doesn't seem to hard            01/01/70 00:00      
      D+ and D- is not differential at the begining            01/01/70 00:00      
      nope, II            01/01/70 00:00      
   re: autodetect            01/01/70 00:00      
   I bought on of these at radio shack.            01/01/70 00:00      
      speed detect            01/01/70 00:00      

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