# Control Unit - Q10

+1 vote

A control system uses a control memory of 1024 words of 32 bits each. The microinstruction has three fields which are shown below.

Control word

 Control Signals Status Bits Next Address

The no of different control signal combinations in the system is 131. If vertical microprogramming is used then maximum number of status bits we can have is ---?

reshown Jun 9

The answer is 14
answered Jun 9 by (1,640 points)

Vertical Microprogramming used so control bits = $log_2{131} = 8$

 $\log_2(131) = 8$ $\log_2(S)=s$ $\log_2(1024)=10$

Control memory size given,

${1024\times 32} = 2^{15}bits$ or $2^{12} Bytes$

Control word size = total bits = 8+s+10

Control memory = $\frac{\text{Control Word Size} \times \text{\# of words}}{\text{Byte size}}$

$2^{12} = \frac{(18+s)\times 2^{10}}{8}$

$2^{15} = (18+s)\times 2^{10}$

$32= 18+s$

$s= 14$

So status bits = 14

answered Jun 9 by (4,120 points)