4 Internal Digital IC Faults Malfunction in the internal circuitry-cause by one of the internal component failing or operating outside its specificationInputs or outputs shorted-input to be stuck either high or lowInput output open-circuited-stuck to high or low IC outputShort between 2 pins (other than ground or VCC- IC force 2 pins to be always identical
11 Memory TerminologyMemory Cell- a device or electrical circuit that can store a single bitMemory Word- A group of bits in a memory that represents information or dataByte- 8 Bit WordNibble-a 4 bit binary numberCapacity- specify how many bits can be stored in a particular memory device.Density-another term for capacityAddress-this is a number that identifies location of a word in memory.Read Operation Binary word stored in a memoryWrite operation- a word is placed into a particular operationAccess Time- memory device operating speedRAMSAMRWM
12 Continuation..Static Memory Device-a semiconductor device that stored data permanentlyDynamic Memory Device-a device that will not stored data permanentlyInternal Memory-computer main working memoryAuxiliary Memory-Mass storage store amsiva amount of information
13 Input and output Lines perform by a memory Select the address in memory that is being accessed for Read or WriteSelect either Read or Write operation to be performedSupply the input and data to be stored in the memory during a write operationHold the output data coming from memory during a read operationEnable or (disable) memory so that it wil no respond to the address inputs and read write commands
15 Problem 1A certain semiconductor memory chips is specified as 2k X 8. How many words can be stored on this chips? What is the word size? How many total bits can this chips store? Given: Number of words in a memory is often 1024 = 1K2K = 2 X 1024 = 2048 wordsEach word is 8 bits ( one byte) The totalnumber of bits is therefore2048 X 8 = 16,348 bits
16 Problem 2 A certain memory has a capacity of 256K X 8. How many data input and data input does it have?How many address lines does it have?What is its capacity in bytes?
17 Solution A) Eight of each, since the word size is eight. B) The memory stores 256 =256 X 1024= 262,144 words. Thus, there are 262,144 memory addresses. Since 262,144 = 2 it requires 8 bit address code to specify one of 262,144 addressesC) a byte is 8 bits, this memory has the capacity of 262,144 bytes18
19 The READ operationThere are 16 data words stored at 16 different address location.Examplelocation 0011 is this data is stored in binary inside ROM
20 ROM ArchitectureInternal structure of a ROM IC is very complex (recommendation need not to know the details)Four basic parts of ROMRow decoderColumn decoderRegister array- register data that has been programmed into ROMAnd output buffers.
22 Address DecoderDetermines which register in the array will be enabled to place its 8 bit data word into the bus.Example 1What register will enabled by input address 1101?Ans. A3 A2 = 11 will activate column 3A1 A0 = 01 will activate the row 1 select line.
23 Example 2 What input address will enable register 10? Ans. A1 A0 = 10 and A3 A4 = 10Therefore A3 A2 A1 A0 = 1010
24 Output buffersData is feed into the output buffers, which will pass the data into the external data outputs provided that CS is low. If CS is High the output buffers are in high Z state and D0-D8 will be floating.Example: Intel 2708 is a MOS ROM that stores bit words. Its 1024 registers are arrange in a 64 X 16 array.In practice ROM capabilities typically range from 32 to over 1 M bytes
25 ExampleDescribe the internal architecture of a ROM that stores 4K bytes and uses a square register array.Solution4K is = 4 X 1024 = 4096 therefore it holds bits words.Since 4096 = 64 the register are arrange by 64 by 64 arrayThere are 64 rows and 64 columnThis requires 1 of 64 decoder to decode the six address for the row selectAlso 1-of-64 decoder to decode the six address inputs for the column selectThus the total of 12 address inputs are requiredTherefore since 2 = 4096 proving that there are 4096 different address212
26 Types of ROMMask Program ROM-has its storage location written into (programmer) by the manufacturer according to customer’s specifications.
31 Cont… Erasable programmable ROM (EPROM) Can be program by the user and it can be erased also as often desired.Once programmed, the EPROM is a nonvolatile memory that will hold its desired data indefinitelyTo erase the program exposed to UV lightAvailable with a capacity of 128K X ns Example: Intel 2732 is a 4k X8 NMOS EPROM
34 Cont…. Electrically Erasable PROM (EEPROM) Retains the same floating-gate structure as the EPROMDeveloped product of EPROM (100 ns)Has the ability to electrically erase and rewrite individual bytes (8 bit words) in memory during the arrayDuring the write operation internal circuitry automatically erases all the cells at an address location prior to writing the new data Example: Intel K X 8 array with 13 address inputs (2 = 8292) and 8 data I/O pins13
42 ROM ApplicationFirmware- storage of data and program codes that must be available on power-up in microprocessor-based systemsData Tables- used in trigonometric tablesData Converter- data is expressed in one type of code and produces an output expressed in another type