Ferguson Institute Online Div. of Jmlit
Assignment #3a

THE MAIN SECTIONS OF THE CPU - THE MICROPROCESSOR:

The main microprocessor "chip" decodes & executes computer program instructions.
CONTROLLER-SEQUENCER:  The actual fetching and execution of instruction like IN, OUT, ADD , COMPARE, MOVE, as a binary word and copies it into the instruction register.  A crystal regulated timing signal is used to "clock"  each program instruction stored at a specific address in ram into the instruction register.  From this location, the instruction, in binary form, which is a series of o's and 1's (actually high and low voltage signals) is sent to the decoder.  Some instructions like IN and OUT generate control signals like read and write thats later used as a part of a three state data transfer, from a register in/out to/from an external i/o port or ram chip.

DECODER:    The decoder "looks" at the combination of 0's and 1's and decides which system microprograms to execute.  A different set of microprograms are selected for each specific instruction.  Many 0s and 1s bits are decoded into one output line leading to a certain set of microprograms. 

ARITHMETIC-LOGICAL UNIT:  Instruction or opcodes like ADD , COMPARE, have microprograms that engages a section of the microprocessor called the ALU.  Then microprogram processes the data portion of the instruction called the operand.  The results of these calculations are placed into one of the main registers on the microprocessor chip.
Most importantly, the state of the microprocessor is recorded and placed into a special register called the control register or the flag register.  Various ALU operations set flags  including the carry flag, the half carry flag, the negative results flag, the overflow flag, and the zero results flag.  These flags may be used to verify the correctness of the operation.  Student should perform binary addition, subtraction, mutiplication, comparisons problems, etc. and observe the results appearing in the control register.  Calculation should first be done by hand and then done automatically with the Debugger program or one of many free downloadable stepper programs that show the results after each program step.
MEMORY ADDRESS REGISTER:  This register which is a series of flipflops which latches its results until an external clocking signal changes its output.  It si called the memory address register because the hexadecimal number is the location of the next program instruction to be executed.
CONTROL FLAG REGISTER:  See Dvd1.

OPEN THE DVD SET "JML1" and place it in the dvd drive and run it.  Take notes on this material that covers this secion.