Lecture 4

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Unformatted text preview: rface hardware (e.g., registers), try to share registers if possible but beware of unwanted interactions if a signal goes to more than one device If out of ports, must force sharing by adding hardware to make a dedicated port sharable (e.g., adding registers and enable signals for the registers) If still run out of ports, then most encode signals to increase bandwidth (e.g., use decoders) If all else fails, then backup position is memory-mapped I/O, i.e., what we would have done if we had a bare microprocessor " %+ 5 % $ . 0 ' %+ . 0 & We need 8 8-bit registers to store/write the 64 bits Suppose we wanted a 64-bit I/O port If EN is true, then we have an output pin If EN is false, then we have an input pin Select the EN addresses to be $...000 to $...007 Select OUT addresses to be $...010 to $...017 Read 15th bit load value at address $...011 (2nd set of OUT regs) logical AND with 0x80 bit position 7 of result is 15th bit Write the 47th bit read OUT register at $...015 set bit position 7 to desired value ( or with 0x80) store in $...015 load EN re...
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This document was uploaded on 04/04/2014.

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