Page 215 -

5.5 / KEY TERMS, REVIEW QUESTIONS, AND PROBLEMS 183

5.7 Figure 5.17 shows one of the early SRAMs, the 16 * 4 Signetics 7489 chip, which
stores 16 4-bit words.
a. List the mode of operation of the chip for each CS input pulse shown in
Figure 5.17c.
b. List the memory contents of word locations 0 through 6 after pulse n.
c. What is the state of the output data leads for the input pulses h through m?
5.8 Design a 16-bit memory of total capacity 8192 bits using SRAM chips of size 64 * 1 bit.
Give the array configuration of the chips on the memory board showing all required
input and output signals for assigning this memory to the lowest address space. The
design should allow for both byte and 16-bit word accesses.
5.9 A common unit of measure for failure rates of electronic components is the Failure
unIT (FIT), expressed as a rate of failures per billion device hours. Another well
known but less used measure is mean time between failures (MTBF), which is the av-
erage time of operation of a particular component until it fails. Consider a 1 MB
memory of a 16-bit microprocessor with 256K * 1 DRAMs. Calculate its MTBF as-
suming 2000 FITS for each DRAM.
5.10 For the Hamming code shown in Figure 5.10, show what happens when a check bit
rather than a data bit is in error?
5.11 Suppose an 8-bit data word stored in memory is 11000010. Using the Hamming algo-
rithm, determine what check bits would be stored in memory with the data word.
Show how you got your answer.
5.12 For the 8-bit word 00111001, the check bits stored with it would be 0111. Suppose
when the word is read from memory, the check bits are calculated to be 1101.What is
the data word that was read from memory?
5.13 How many check bits are needed if the Hamming error correction code is used to de-
tect single bit errors in a 1024-bit data word?
5.14 Develop an SEC code for a 16-bit data word. Generate the code for the data word
0101000000111001. Show that the code will correctly identify an error in data bit 5.