8085 processor. Bus system in microprocessor. Intel 8085 Block Diagram. Intel 8085 Signals. Stored program organization. Basic computer registers and memory. List of Registers for the Basic Computer. Computer Instructions. each computer has its own unique instruction set.
each computer has its own unique instruction set.
The basic computer has three instruction code formats
2) The register-reference instructions
are recognized by the operation code 111 with a 0 in the leftmost bit (bit 15) of the instruction
3) input-output instruction
are recognized by the operation code 111 with a 1 in the leftmost bit (bit 15) of the instruction
to be the address of the operand in a computation-type instruction.
Thus the effective address in the instruction in memory address 22 is 457
and the effective address in the instruction in memory address 35 in the instruction is 1350.
The microoperations for the fetch and decode phases can be specified by the following register transfer statements
SC is cleared to 0
T0: AR PC
T1: IR M[AR], pc pc+1
T2 : D0,.D7 Decode IR(12-14), I IR(15),
Example of BSA instruction execution
Control unit of basic computer
It consists of two decoders, a sequence counter, and a number of control logic gates.
An instruction read from memory is placed in the instruction register (IR).
Circuits associated with AC
In order to design the logic associated with AC, it is necessary to go over the register transfer statements as shown and extract all the statements that change the content of AC.
The control function for the clear microoperation is rB11 where r = D7 I T3 and B11 = IR (11).
Output of OR Gate in the last fig.