The central processing unit – Execution of programs
(a) The diagram shows the flow of data in a computer system. In which part would you expect to find the Immediate Access Store?
(b) Give one use for the Immediate Access Store.
(c) (i) An instruction word has been copied from the Immediate Access Store under the direction of the control unit. Where would it have been copied to?
(ii) What part does the program counter play in the above event?
(d) Some instructions make use of the accumulator. Describe briefly one use of the accumulator.
JOB Indicate the function of the Sequence Control Register and the Instruction Register in the CPU.
Describe a typical fetch-execute cycle in the execution of a program instruction, with particular reference to these two registers.
Complete the following table by filling in the correct instruction type chosen from the list.
arithmetic logic control data transfer
|
instruction |
Type |
|
Save |
|
|
Or |
|
|
Jump |
|
|
Subtract |
26 MEG1988,Paper2No4 A computer uses a word length of 8 bits. Machine code instructions are represented by 3 bits for the operation code followed by 5 bits for the address.
The instruction JUMP 23 is represented by:
|
1 |
0 |
1 |
1 |
0 |
1 |
1 |
1 |
operation code address
(a) How many different addresses can be directly addressed?
(b) Most programmers would prefer to write the instruction JUMP 23 as JUMP start.
(i) Give one advantage of using a name such as start.
(ii) Name the system software which would convert the instruction JUMP start into machine code.
(c) The computer stores numbers in two’s complement form. The number + 15 is stored as:
|
0 |
0 |
0 |
0 |
1 |
1 |
1 |
1 |
Fill in the diagram below to show how -15 would be stored.