Chapter 3 · Watch, then practise
Control Unit
Study how control sequences are represented, selected and executed.
3 questions · 3 with related videos. Matches are based on playlist titles; broader background matches are labeled.
What to study
- Hardwired control
- Microinstructions
- Control memory
- Microprogram sequencing
Chapter playlists
Control Unit — existing playlist
Hardwired CU vs Micro-programmed CU | COA | Computer Organization and Architecture Lecture
Last moment tuitions · 11:16
Compares the two control-unit strategies asked about in this question.
1. Two control strategies
How do hardwired and microprogrammed control represent an instruction sequence?
Hardwired control realizes the sequence through logic and state transitions. Microprogrammed control stores control words in a control memory and steps through them using a microprogram counter. Microcode can simplify complex sequences; its storage and sequencing also have costs. Actual processors can combine both approaches.
Microprogram sequencer-lecture27/coa
asha khilrani · 14:46
Related microprogram-sequencer lesson for choosing the next microinstruction.
2. Control sequencing
What selects the next microinstruction?
Possible choices include the next sequential control-memory address, an opcode-dependent entry point, a conditional target, or the current address while waiting for memory. A microinstruction therefore describes both datapath actions and how execution continues. A machine instruction may require several such microinstructions.
Microinstruction Formats(part1)- lecture21/coa
asha khilrani · 12:53
Choose a video · 2 lectures
These microinstruction-format lessons support the discussion of encoded control signals.
3. Horizontal and vertical microcode
What is traded when control signals are encoded into a narrower microinstruction?
Horizontal microcode uses wider words that can express several compatible actions together. Vertical microcode encodes actions more compactly, usually requiring decoding and potentially more steps. Compare total control-store size, permitted parallel operations and sequence length, rather than word width alone.