A computer uses a memory of 65,536 words with eight bits in each word. It has the following registers: PC, AR, TR (16 bits each), and AC, DR, IR (eight bits each). A memory-reference instruction consists of three words: an 8-bit operation-code (one word) and a 16-bit address (in the next two words). All operands are eight bits. There is no indirect bit. 

a. Draw a block diagram of the computer showing the memory and registers as in Fig. 5-3. (Do not use a common bus). 

b. Draw a diagram showing the placement in memory of a typical three-word instruction and the corresponding 8-bit operand. 

c. List the sequence of microoperations for fetching a memory reference instruction and then placing the operand in DR. Start from timing signal T₀.

Fig. 5-3

 

Transcribed Image Text:

15 15 7 OUTR 11 11 IR TR 0 7 PC AR INPR 0 0 0 15 15 Memory 4096 words 16 bits per word DR AC