Using the 3-variable multiplexer chip of figure 3.12 (pp. 161 in the textbook 1, 6/e), implement a function whose output is the odd parity of the inputs. That is, the output is 1 if and only if an odd number of inputs are 1. A common chip is a 4-bit adder. Four of these chips can be hooked up to form a 16-bit adder. How many pins would you expect the 4-bit adder chip to have? Why? (Draw a diagram of a 4- bit adder). SEC. 32 BASIC DIGITAL LOGIC CIRCUITS 161 Di paralkel-to-serial data comerter By putting 8 bits of data on the input lines and den stepping the coatrol lines seuecially from INX0 to 11 binary the 8 hits are put onto the output line in serie A pical us for puralled-4o-erial comvension is in a keyboard. where each keystroke implicitly defines a 7-or 8-bit sumber that must be outpt over a scrial link, such as USB The inverse of a multipleser is a demultipleser. which routes its single input igaal to ce f 2" outpus, depeng on the values of the& comsol lnes e binary value on the control lines isk,output&is selected As a second cxample, we will now look ; a circuit that takes an/-bit number as input and uses it to select (Le., set 1)esactly one of the 2" output lines Such a einit illustraled for-3in Fig. 3-13, is called a deceder To see where a decoder might be useul, imagine a small memory consisting of eight chips each coaaining 236 MB. CpO has addresses 0 to 236 MB, chip I has addresses 256 MB to 512 MB. and 50 when an address is presented to the memory, the high-osder 3 bis are sed o select one of the eight chip Using th eircuit of Fig. 3-13, these 3 bils are the three inpats, A. B and C Dpnding on the inputs, exactly one of the eight ouput lines,..D.is 1:che rest are 0 Each output line enables on of the eight memory chips, Becnse only one output line is set to I, only one chip is emabled 162 THE DIGITAL LOGIC LEVEL CHAP 0 0