ENGR 100 1 Peter Chen
Implementing combinational and sequential
logic
We’ve used combinational logic, registers, and memory as
building blocks in our digital circuits
Specified the behavior of combinational logic as truth table
and in Verilog
• now we’ll implement arbitrary combinational logic
blocks with transistors
Specified the behavior of registers and memory
• now we’ll implement a register with combinational logic
and feedback
Overview of implementing combinational logic
• implement simple combinational logic functions (AND,
OR, NOT)
• combine these to implement arbitrary combinational
logic blocks
Transistors
Transistor is a controlled switch
• switch can be connected (source data flows to output
data) or disconnected (source data does not flow to out-
put data)
• state of the switch depends on a control input
p-type transistor
• if control input = 0, then output is connected to source (1)
• if control input = 1, then output is disconnected
n-type transistor
• if control input = 0, then output is disconnected
• if control input = 1, then output is connected to source (0)
p-type
1
control input
output
n-type
0
control input
output
