26 votes 26 votes Find out the width of the control memory of a horizontal microprogrammed control unit, given the following specifications: $16$ control lines for the processor consisting of ALU and $7$ registers. Conditional branching facility by checking $4$ status bits. Provision to hold $128$ words in the control memory. CO and Architecture gate1987 co-and-architecture microprogramming descriptive + – makhdoom ghaya asked Nov 11, 2016 • recategorized Apr 22, 2021 by Lakshman Bhaiya makhdoom ghaya 5.8k views answer comment Share Follow See all 2 Comments See all 2 2 Comments reply Aalok8523 commented Aug 11, 2020 reply Follow Share As in question "horizontal micro-programmed control unit" is told that's why we can't use decoder to decrease required number of status bits (like we do in vertical miro-programmed control unit). So, we need 4 status bits in "control word" register. Let me know if i am wrong ? 3 votes 3 votes Pranavpurkar commented Dec 6, 2022 reply Follow Share @Aalok8523 This is saying the same thing https://www.geeksforgeeks.org/difference-between-horizontal-and-vertical-micro-programmed-control-. 0 votes 0 votes Please log in or register to add a comment.
Best answer 21 votes 21 votes Width of the control memory $=$ size of a control word $\text{Control word} = [\text{Condition bits} + \text{control signal bits} + \text{next address}]$ Condition bits $= 4 \implies \log_2 4$-bits $128$ words $\implies 7$-bits for address. In the case of horizontal micro-programming, there is $1$- bit for each control signal. It is given there are $16$ control signals. $\implies$ Length of control word $= 2+16+7 = 25$- bits. agoh answered Jan 22, 2017 • selected May 26, 2022 by Arjun agoh comment Share Follow See all 16 Comments See all 16 16 Comments reply Show 13 previous comments Ajit_Singh commented Dec 16, 2020 reply Follow Share Somebody plzz explain..why are we not considering the 7 registers ? what is their use in this question ?? 2 votes 2 votes jaswanth431 commented Sep 7, 2021 reply Follow Share @Ajit_Singh 7 registers are nothing to do with the given question , they just describe that processor consists of ALU and 7 registers. They just want to confuse us with extra information. 1 votes 1 votes Pranavpurkar commented Dec 6, 2022 reply Follow Share @jaswanth431 see here, for both horizontal and vertical ,there is different criteria for selecting the flag bits,in case of horizontal all the bits are taken , and in vertical log(n) bits are taken(where n are no. of status bits) https://www.geeksforgeeks.org/difference-between-horizontal-and-vertical-micro-programmed-control- so according to this , answer for this question must be $27$ bits. 0 votes 0 votes Please log in or register to add a comment.
15 votes 15 votes .... Hira Thakur answered Nov 3, 2017 Hira Thakur comment Share Follow See all 0 reply Please log in or register to add a comment.
4 votes 4 votes 16 bits for 16 control lines.(As Horizontal) For next address field 7 bits (128 control words.. 2^7=128) 4 status bits. Width of control memory = control word length = 4+16+7 = 27 bits Dipmukherg answered Aug 8, 2017 Dipmukherg comment Share Follow See all 3 Comments See all 3 3 Comments reply chauhansunil20th commented Oct 17, 2018 i edited by chauhansunil20th Oct 17, 2018 reply Follow Share No, $25$ bits will be the correct answer, as we need only 2x1 MUX for 4 status bits. 3 votes 3 votes Gurdeep Saini commented Nov 23, 2018 reply Follow Share :https://gateoverflow.in/1061/gate2004-67 watch this 25 is correct 1 votes 1 votes vizzard110 commented Jul 21, 2019 reply Follow Share Correct me if I am wrong. In the question https://gateoverflow.in/1061/gate2004-67 It is not given that it is a horizontal microprogrammed unit. Then how can we apply that logic to this question. 1 votes 1 votes Please log in or register to add a comment.