2. • What is Read only memory (ROM)?
• What is Programmable Logic Array?
• What is Synchronous Sequential Logic?
3. READ ONLY MEMORY (ROM)
• Is a class of storage medium used in computer and other electronic devices. Data
stored in ROM can’t be modified or can be modified slowly or with difficulty.
• is a fixed array of AND gates and a programmable array of OR gates
• Read Only Memories (ROM) have:
• N input lines
• 2N decoded minterms.
• M output lines
8. WHY IS ROM NON- VOLATILE
•ROM stores data and instructions permanently.
When the power is turned off, the instruction
stored on ROM are not lost
9. TYPE OF ROM:
• Programmable read only memory (PROM)
• Erasable Programmable read only memory (EPROM)
• Electrical Erasable Programmable read only memory
(EEPROM)
10. PROGRAMMABLE ROM (PROM)
• Is a read only memory that can be programmed directly by the
user using a special PROM programmer. It is also sometimes
called a fusible-link PROM.
• The data in them is permanent and cannot be change. PROMs
are used in digital electronic devices to store permanent data,
usually in low level programs such as firmware.
11. ERASABLE PROGRAMMABLE ROM (EPROM)
• It is a type pf memory chip that remains its data when its power supply is
switched off.
• Once programmed, EPROM can be erased by exposing it to strong ultra
violet light.
• EPROMs are easily recognizable by the transparent fused quartz window in
the top of the package, through which the silicon chip is visible and
permits exposure to ultraviolet light during erasing.
12. ELECTRICAL ERASABLE PROGRAMMABLE ROM (EEPROM)
• Also can be written as E²PROM and pronounced e-e-prom, double-e-
prom or e squared-prom.
• EEPROM are organized as arrays of floating-gate transistors. It can be
programmed and erased in-circuit, by applying special programming
signals.
• It has a limited life for erasing and reprogramming.
• EEPROM typically allows bytes to be read, erase, and rewritten individually.
13. DIFFERENCES OF PROM AND EPROM
• PROM is the older technology.
• PROMs can be only programmed once while EPROMs are
reusable and can be programmed multiple times.
14. DIFFERENCE OF EEPROM AND EPROM
• EPROM is the older technology.
• EPROMs have to be erased with the exposure of UV light and
EEPROMs can be erased electronically.
15. PROGRAMMING LOGIC ARRAYS (PLA)
• a programmable array of AND gates feeding a programmable array of OR
gates.
• Compared to a ROM, a PLA is the most flexible having a programmable
set of ANDs combined with a programmable set of ORs.
19. SYNCHRONOUS SEQUENTIAL LOGIC
• an electronic oscillator called a clock (or clock generator)
generates a sequence of repetitive pulses called the clock
signal which is distributed to all the memory elements in
the circuit.
• Signals affect the memory elements at discrete instants of
time.
• Discrete instants of time requires synchronization.
• Synchronization is usually achieved through the use of a
common clock.
20. SYNCHRONOUS SEQUENTIAL LOGIC
• Circuits are easy to design
• Clocked flip flop acts as memory element.
• The status of memory element is affected only at the active
edge of clock, if input is changed.
21. ASYNCHRONOUS SEQUENTIAL CIRCUITS
• If some or all the outputs of a sequential circuit do not change affect with respect
to active transition of clock signal, then that sequential circuit is called
as Asynchronous sequential circuit.
• That means, all the outputs of asynchronous sequential circuits do not
change affect at the same time. Therefore, most of the outputs of asynchronous
sequential circuits are not in synchronous with either only positive edges or only
negative edges of clock signal.
