Systems & Networks

There was a quick summing up of the differences between CISC (Complex Instruction Set Computing) and RISC (Reduced Instruction Set Computing) CISC (Intel PC) Wide range of OP codes Variable length instructions RISC (Sun SPARC, ARM) Operands pre-fetched into registers Only LDA & STA can reference memory mem to reg or reg to mem LDA & STA use Indirect, Indexed Addressing with Base Address and the Index in registers All other instructions operate on registers 64 registers only requires 6 bit address

Then we had a go at working out the addressing schemes using the following memory set up with the next ten questions.

Location	50	60	65	70	85	90	95	98	99	X
Content	85	80	444	555	60	222	111	60	50	10

The idea is to work out what is in the Accumulator after fetching and executing the LDA instruction with the addressing scheme indicated. Remember that there are 4 different addressing schemes as follows:

LDA 75	Direct Addressing	Put contents of 75 into Acc
LDA #75	Immediate Addressing	Put 75 into Acc
LDA *75	Indirect Addressing	Data is in Address found in 75
LDA @75	Indexed Addressing	Add Index Register to 75 to get Data Address
LDA #6,75	Offset Addressing	Add 6 to 75 to get Data Address (81)

The questions are:
LDA #50	Acc=?
LDA 50	Acc=?
LDA @55	Acc=?
LDA @80	Acc=?
LDA *50	Acc=?
LDA *85	Acc=?
LDA *@99	Acc=?
LDA *@98	Acc=?
LDA @*88	Acc=?
LDA @*75	Acc=?

Scroll down for the answers:

Answers

1=50

2=85

3=444

4=222

5=60

6=80

7=80

8=555

9=80

10=80

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