RS latch
bistable circuit, meaning it can happily exist in either of 2 stable states, with the ability to store its last output.
latch- it can latch onto incoming data.
D-latch
enables input on a gated S-R latch provides a way to latch the Q and not Q outputs without regard to the status of S or R.
we can eliminate one of those inputs to create a multivibrator latch circuit with no “illegal” input states.
Timing diagram
a type of truth table for sequential logic gates
Clock
- acts as the heartbeat of our system, creating windows of time to write or read to/from our storage devices
- acts like a conductor to synchronize information windows across our CPU.
The D Flip Flop (DFF)
- an edge-triggered device that stores data at the edge of the clock.
- takes a clock input (often denoted with triangle)
Latch vs Flip-flop
Latch is level sensitive and flip flop is edge-sensitive
Registers
collection of latches or flip-flops controlled by a common WE (or CLK)
Finite-state machine (or Finite state automation)
computation model that can be implemented with hardware or software and used to simulate sequential logic and some computer program.
Computer memory
Physical devices capable of storing information temporarily like RAM (random access memory) or permanently like ROM (read only memory)
RAM (Random access memory)
by specifying address, one can read or write to any drawer in the memory at random.
ROM (read-only memory)
non-volatile memory used in computers and other electronic devices to store data permanently. use to hold a small program or setting that a computer might rely on for startup.
What is the hierarchy of Memory in a computer
- CPU
- Cache
- Main memory
- Disks (permanent storage)
Finite state machine (FSM)
A machine that can be built using combinational and sequential logic gates.
what is a toaster?
an example of an FSM with 2 basic states (off and on/warming)
What are 3 basic parts in FSMs?
- An n bit register which stores the state of the machine
- a block of logic that computes the next state as a function of the current state and any inputs.
- a block of logic that computes the output based on the current state.
what happens to the D-latch when the WE is set to high?
D latch is open.
Q follows D
what happens to the D-latch when the WE is set to low?
D latch is closed. Data is stored and read only
The difference between windows of time to store and read information with D-latch and DFF
D latch:
- windows of time to store and read information are equal
- WE = high, d latch opens up. As a result, Q follows D
- WE = low, d latch is closed. Data is stored and read only.
DFF:
- window of time for storage is shorter but more time to read.
- able to store data when the clock transitions from 0 to 1.
- otherwise, DFF is closed and can only read from it.
- we prepare what we wish to store right before the positive edge of the clock.
