Microprocessor Fundamentals Week 3 Mount Druitt College of TAFE Dept. Electrical Engineering 2007

© Mike Stacey 2007 Last week’s prac You should have 2 files saved to your floppy or flash disk: You should have 2 files saved to your floppy or flash disk: Week2.txt: contains a printout of all operations performed within debug for Debug exercises 1 and 2. Also contains answers to questions. Week2.txt: contains a printout of all operations performed within debug for Debug exercises 1 and 2. Also contains answers to questions. Dex1.com: program saved from exercise 2. Dex1.com: program saved from exercise 2. These 2 files must be given to me during week 3 for marking. These 2 files must be given to me during week 3 for marking.

© Mike Stacey 2007 Memory Terminology (p1) RAM: Random access memory. Storage of volatile data – data and program that is currently being used by the processor. Volatile. RAM: Random access memory. Storage of volatile data – data and program that is currently being used by the processor. Volatile. ROM: Read only memory. Data/program that is stored and cannot be changed or overwritten. Non-volatile. ROM: Read only memory. Data/program that is stored and cannot be changed or overwritten. Non-volatile. Write: To store data into memory Write: To store data into memory Read: To extract/read it out of memory Read: To extract/read it out of memory

© Mike Stacey 2007 Types of RAM (p1) RAM RAM Static: storage element is the flip flop. Retains its data (1 or 0) while power is applied. Static: storage element is the flip flop. Retains its data (1 or 0) while power is applied. Dynamic: Uses the capacitor as a storage element. Loses its data if not constantly refreshed. Dynamic: Uses the capacitor as a storage element. Loses its data if not constantly refreshed. Refresh every 2mS Refresh every 2mS More capacity for a given size than static More capacity for a given size than static Cheaper than static Cheaper than static

© Mike Stacey 2007 RAM (p1-p2) Note: For a 4 bit address bus there are 16 addressable locations inside the RAM chip. This is 2 4. Hence we need 4 address lines in the bus. We say the RAM has a capacity of 16Bytes because it can store 1 byte (8 bits in each location). The chip in Fig 3.1 is a 6116 RAM. What is its capacity? R/W: Read Write CS: Chip select OE: Output enable D 0 – D 3: 4 bit data bus

© Mike Stacey 2007 Writing to RAM (p2) Figure 3.2 – Write Cycle Minimum time required to perform a write operation Data is written to the address on the address bus when the R/W line is low and CS is low.

© Mike Stacey 2007 Reading from RAM (p2) Figure 3.3 – RAM Read Cycle Access time is the minimum time between application of address and availability of data at the output Data is read when OE is low and CS is low

© Mike Stacey 2007 ROM (p3) R/W: Read Write CS: Chip select OE: Output enable D 0 – D 7 : 8 bit data bus What is the capacity of this ROM in bytes?

© Mike Stacey 2007 Types of ROM (p3-p4) Mask Programmable ROM: Programmed in factory and program cannot be changed. Mask Programmable ROM: Programmed in factory and program cannot be changed. Fusible Link Programmable ROM (PROM): Can be programmed once Fusible Link Programmable ROM (PROM): Can be programmed once Erasable programmable ROM (EPROM): Can erase by exposure to UV light. After erasure, they can be re- programmed using a special burner. Erasable programmable ROM (EPROM): Can erase by exposure to UV light. After erasure, they can be re- programmed using a special burner. Electrically Erasable Programmable ROM (EEPROM): Can be erased electrically meaning no removal from circuit. Finite number of re-programs. Electrically Erasable Programmable ROM (EEPROM): Can be erased electrically meaning no removal from circuit. Finite number of re-programs. Flash: a type of EEROM. Flash: a type of EEROM.

© Mike Stacey 2007 ROM Applications (p4) Used wherever data needs to be permanently stored. Used wherever data needs to be permanently stored. BIOS (Flash) BIOS (Flash) Decoding Decoding Programs Programs

© Mike Stacey 2007 Terminology (p4) Access Time: the minimum time required to read data from, or write data to memory Access Time: the minimum time required to read data from, or write data to memory Cell: storage for one bit of data Cell: storage for one bit of data Density: the number of cells for a given IC Density: the number of cells for a given IC Dynamic: a form of RAM that requires refreshing Dynamic: a form of RAM that requires refreshing Static: a form of RAM that does not require refreshing Static: a form of RAM that does not require refreshing Location: a group of bits, generally one byte Location: a group of bits, generally one byte Volatile: memory that loses its data when power is removed Volatile: memory that loses its data when power is removed Non Volatile: memory that does not lose its data when power is removed Non Volatile: memory that does not lose its data when power is removed RAM: a form of volatile memory RAM: a form of volatile memory Read: obtain information from memory Read: obtain information from memory ROM: a form of non volatile memory ROM: a form of non volatile memory Storage Capacity: the total number of bits that can be stored in memory, generally expressed in bytes or bits and factors of 2 10 (1024= 1k) Storage Capacity: the total number of bits that can be stored in memory, generally expressed in bytes or bits and factors of 2 10 (1024= 1k)

© Mike Stacey 2007 Typical RAM and Capacities (p5) Number of bits in each location Number of locationsCapacity in bits

© Mike Stacey 2007 Review Questions Do ‘em! Do ‘em!