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EE notes 2_25

EE notes 2_25 - EE 454 right in time vs prematre signaling...

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EE 454 2/25/08 right in time vs prematre signaling of the flag Memory space is much bigger than i/o space. Memory space is ready all the time. I/O devices are conditional ususally (excepty simple LEDs and switches for exaple). Connect switch output directly to mp? No. You put a tristate buffer. Reading or writing switches? Reading, so connect IDSP which has: Read bar, io mem, and address. Use flip flop between memory and led. D gets bufferd data line, q goes to led. If led is sinking mode, you must send a 0. Connect Write bar with ODSP (says write, io, and address). Durring t2 t3, data sent out and activated, data and write bar start together. data is valid and stable before and after write ends. need a low going pulse that replicates the write bar. So we need an ODSP BAR. Conditional device: produces data and strobe. Deposits data and strobe into a latch. There also is a flip flop to indicate when the signal has been sent. Connect ff and latch directly to mp? No add tristate buffers to both connections. The buffers are enabled with READ BAR associated with an
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