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Jan Waclawek
12/13/05 02:30
Read: 708 times
Bratislava
Slovakia


 
#105128 - comparator
Responding to: Suresh R's previous message
The 74HC688 is a comparator, it's output (/P=Q) goes active=low when the P inputs are exactly the same as the Q inputs. You set the Q inputs by the dipswitches and when the same address occurs at the A4-A9 lines on ISA, the /P=Q output goes low. This enables the 74LS138 decoders, so when this address occured simultaneously with /IOR or /IOW active(=low) on the ISA bus, one of the outputs of 74LS138 (according to the state of A0-A3 address) goes low.

So the state of DIPSW determines the bits 4-9 of I/O address space where the card is active (=> "base address"). This is an 8-bit card, the 8-bit in and out instructions issue only 10-bit address on x86.

Jan Waclawek


List of 33 messages in thread
TopicAuthorDate
Add on card programming      Suresh R      12/07/05 03:11      
   please clarify      Jan Waclawek      12/07/05 03:35      
      RE: please clarify      Suresh R      12/07/05 04:35      
         (E)ISA addressing      Jan Waclawek      12/07/05 04:48      
            IOW and IOR      Suresh R      12/08/05 04:52      
               not explicitly      Jan Waclawek      12/08/05 06:02      
                  IRQ in EISA slot      Suresh R      12/09/05 01:05      
                     interrupt      Jan Waclawek      12/09/05 02:21      
                        QBASIC programming      Valentin Angelovski      12/09/05 04:53      
                           reply      Suresh R      12/10/05 04:10      
                              DIP Switch Address Setting in EISA card      Suresh R      12/12/05 03:10      
                                 DIP switches...      Valentin Angelovski      12/12/05 03:55      
                                    card design enclosed      Suresh R      12/13/05 02:10      
                                       comparator      Jan Waclawek      12/13/05 02:30      
                           QBASIC live and well.      Charles Bannister      12/12/05 11:12      
                              NT - not quite      Andy Neil      12/12/05 16:16      
                                 timing in Win?      Jan Waclawek      12/12/05 16:21      
                              QBasic Lives!!!      Valentin Angelovski      12/12/05 17:24      
   refer to 'Barry B Brey'      Abhishek Singh      12/07/05 07:39      
   EISA Bus interfacing      Valentin Angelovski      12/08/05 15:54      
      beware if (E)ISA bus books      Erik Malund      12/09/05 08:11      
   Try this?      Andy Neil      12/14/05 15:16      
      Power resistor selection      Suresh R      12/16/05 04:52      
         dont do it      Erik Malund      12/16/05 06:39      
            LM317 is an option      Abhishek Singh      12/16/05 07:46      
               Wasteful!      Andy Neil      12/16/05 09:34      
                  if op can...........      Abhishek Singh      12/17/05 07:16      
                     Power!      Andy Neil      12/17/05 08:27      
         basic Ohm's law      Andy Neil      12/16/05 09:40      
            Trouble shoot      Suresh R      12/19/05 05:13      
               heating      Terry Lingle      12/19/05 07:08      
                  Reply : Heating      Suresh R      12/20/05 04:29      
                     if you refer to D4 then      Erik Malund      12/20/05 06:12      

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