Ferguson Institute Online Div. of Jmlit

Assignment #13

3State Data Tranfer:  (Download or Play DVD#2 titled "3state")

1.  Before can we understand how to transfer data out of the computer we need to recall two previously discussed concepts.  First recall that the current instruction opcode held in the instruction register is processed by the decoder and the controller sequencer, generating microfunctions and control signals.   Secondly, it is these same control signals that are used to select which chip, exterior to the microprocessor,  that data will be sent to or loaded from.  Some form of these control signals are multiplexed or/and wired to the exterior chip's chip-sect pins.

2. MEMORY MAPPING: See DVD#3.

In order for an event to occur (programmed I/O)   ,  3 conditions must exist.  In our example the conditions are as follows:
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A.  The destination address portion of the present READ or WRITE instruction's is placed on the address bus and must be the address of the IC chip we want to read from or write to.  In our example are two addressable IC chips; the decoder chip and the I/O port chip.  

B.  The decoded instruction must activate the proper control line on the control bus.

C.  The data must be on the data bus.
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2.  Take notes on the DVD lecture.

3.  Email a copy of those notes to: ???????@joes-mall.com