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ee454 notes 2_20

ee454 notes 2_20 - EE 454 Notes Input/Output 64K A19 A16 =...

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EE 454 Notes 2/20/08 Input/Output 64K A19 - A16 = 0 A0 - A19 = address line Mutually exlusive? OK, but we don't want to do this, because it increases cost and decreases speed. You need to do this for certain cases though. Memory mapped I/O. Any input device should only give information when the processor wants it. IDSP(input device select pulse). Switches (read) (recieving information so a tristate buffer that loops around is used) -when you use the buffer you can read any time you want...good. -when you have a producer and a consumer you need storage LEDs (write) Sinking or Sourcing mode? Buffer or Register? -Sinking is better -You need to use a register and a buffer that points right. Exercise (5-5) in notes: BA15 = 1; BA14 = 0; -When the data is garunteed valid and stable, displayed on LEDS. -Put a tri-state buffer to garuntee validity at the input or output? NONE. You do not need one! IDSP8000h - Switches (ReadOnly) ODSP8000h - LEDS (WriteOnly) no confusion. -Register or latch is required in the case of output port. Trisate buffer needed for input ports.
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