・各種回路の P し A 化 先月号に引き続き , 現在 , 比較的ポピュラーないく つかの論理回路について , どのように P L A イ匕される かを述べていきます . 今月は特に , 我々の身近にある T T L S S I , M S I ゲートのいくっかを具体的に あげてみます . ①デコーダの p L A 化 T T L のデコーダについては , 以下のように比較的 多くのファミリーがあります . 7442 BCD to Decimal Decoder EXCESS-3 to Decimal Decoder 7443 EXCESS-3-GRAY to DecimaI Decoder 7444 7442 の Open CoIIecter タイプ 7445 BCD to 7 Segment Decoder/Driver 7446 BCD to 7 Segment Decoder/Driver 7447 BCD to 7 Segment Decoder/Driver 7448 BCD to 7 Segment Decoder/Driver 7449 BCD to Decimal Decoder/Driver( ニキシ管ドライプ用 ) 741 引 BCD to DecimaI Decoder/Driver(o/c) 74145 BCD to 7 Segment Decoder/Driver 74246 BCD to 7 Segment Decoder/Driver 74247 BCD to 7 Segment Decoder/Driver 74248 BCD to 7 Segment Decoder/Driver 74249 BCD to 7 Segment Decoder/Driver 74347 BCD to DecimaI Decoder/Driver 74445 BCD to 7 Segment Decoder/Driver 74447 ・・ - , マイコン“第 2 章 マイクロコンビュ - タの基礎回路 第 P し A とマイクロプログラム ■小林昭夫■ 図 1 7442 ( BCD to Decimal Decoder) の仕様 ・真理値表 OUTPUTS D C B A 0 1 2 ー 3 4 , 5 6 7 8 9 、 INPUTS ・論理回路図 OUTPUT 0 ー NPUT A OUTPUT ー ( 3 ) OUTPUT 2 OUTPUT 3 ー NPUT B OUTPUT 4 ・ピン配置図 INPUTS M00 A B C D 9 1 5 1 4 1 3 12 1 1 OUTPUT 5 OUTPUTS INPUT C OUTPUT 6 OUTPUT 7 02 ) ー NPUT D A B C D OUTPUT 8 0 1 2 3 4 5 6 7 8 9 OUTPUT 9 OUTPUTS ー 8 ー
図 2 7447 ( BCD to 7 Segment Decoder/Driver) の仕様 ・ピン配置図 ・論理回路 OUTPUTS b C INPUT INPUT OUTPUT a 田国旧旧田 9 OUTPUT 1 2 a b 0 d e B C CTRHORHL ( 2 ) INPUT ー NPUT OUTPUT 1- 0 -1 ・・ 1 ・ 0 ー - 1- 0 1 0 1 1 0 1 一・ー一 0 4 OI < W 理 真一 1 0 ー 1 0 ー 0 1 1 1 0 0 0 1 0 0 0 1 0 1 0 - ー - 0 ー 0 ・ 1 0 1 0 1 0 - ー一 GND ( 6 ) OUTPUT BI/RBO BLANKING INPUT OR RIPPLE-BLANKING OUTPUT OUTPUT OUTPUT LAMP-TEST ( 3 ) INPUT RBI RIPPLE-BLANKING INPUT ロ目目冒圄圄園当住ロ OUTPUT * O/C ・ 7 セグメント LED 表示 6 8 7 5 4 3 2 0 1 図 3 7442 と等価な PLA このうち , マイコンのアドレス・デコーダとして比 較的良く使われる 7442 ( 図 1 ) と , 7 セグメント L E D をドライプするための代表的 I C として 7447 ( 図 2 ) に ついて各々 P L A 化を考えてみましよう . 7442 は出力が負論理で出ているため , A N D ー 0 R ゲ ートで構成する P L A では出力にインバータを 1 つ付 加しなけれはなりません . 図 3 でおわかりのように O R ゲートは 1 本すっしか使用しないので , 少々もっ たいないような気がします . A N D ゲート部は 7442 と同様なやり方で , 0 ~ F ま でダイオードを配置します ( 図 4 ). 0 R ゲート部は真 図 4 7447 と等価な PLA INPUT A INPUT B INPUT C INPUT D OUTPUT OUTPUT OUTPUT OUTPUT OUTPUT OUTPUT OUTPUT OUTPUT OUTPUT OUTPUT 理値表に従って - 1 ' ' のところにダイオードを配置します . 2 マルチプレクサの P L A 化 マルチプレクサ , またはデータ・セレクタのファミ リーを以下に示します . 3 to 8 DemuItipIexer 74138 DuaI 2 to 4 Demultiplexer 74139 16 to 1 Data Selector 74150 8 to 1 Data SeIector 74151 8 to 1 Data SeIector 74152 0 1 2 3 4 5 6 7 8 9 加ⅱ 15 INPUT A INPUT B 」 T C INPI 」 T D OUTPUT a 侊」 T b 0 」 T 」 T c OUTAJT d 0 」 T 乳 e OUTPt 」 T f TPt 」 T g オープン・コレクタ・タイプの インバータ
す多角形 Polygons 歴 史 Skim the Words 多角形 polygon [påligdn / -95n ] ロ 線分 line segment [ 1 凾 n ségmont] ロ ( 多角形の ) 辺 ロ side [såid] 角度 ロ angle [ 由 1 ] 対角線 ( の ) diagonal [daiéganl] ロ 三角形 ロ triangle [ t 語油 9g1 ] 四角形 quadrilateral 玉 w 記 ro taro ロ ロ 五角形 pentagon [péntogdn / -90 司 ロ 六角形 hex a go n [héksogon / -99n ] ロ 七角形 hepta go n [ hép ね 90n / - gon] ロ 八角形 ロ 0 c tago n [åktogdn / -90n ] 九角形 no n a go n [nånogdn / -99n ] ロ 十角形 ロ decagon [ d6k990n / -99 司 長方形 ロ rectangle [ rékt 由 991 ] ひし形 ロ rhombus [råmbos] 正方形 square [skwéor] ロ perimeter [porfmotor] 周 : 周囲 ロ 面積 ロ area 陸 ari 司 縦の長さ ロ length [ 1 匈ん田 横の長さ ロ width [wfd0 、 wft0] 底辺 ロ base [béis] 面 ロ face [féis] 掛ける , 倍 ロ times [tåimz] ロ height [håit] 円錐 ( えんすい ) ロ co e [k6un] 角柱 prism [prizm] ロ 角錐 ( かくすい ) pyramid [pfromid] ロ 円柱 ロ cylinder [sflindor] 球 ロ sphere [sffor] 数学 国語表現 理 科 課外授業 109
索 引 Apple Ⅱ・ Apple Macintosh ・・ application programming interface ・ Symbol . /kern ・ . config ・ /. config ・ /sbin/init ・ #include ・ 0 で除算・ ・・ 83 , 122 ・・ 68 , 257 2.8BSD ・・ 2BSD ・ 3.3BSD ・ 32000 32 ビット保護モード・ 386BSD ・ 386BSD From the Inside-Out ・ 386BSD Reference CD-ROM ・ ・・ 69 , 303 ・・ 80 , 240 ・・ 28 , 31 , 136 , 173 , 353 , 442 ・・ 38 , 107 ・・ 38 , 444 386BSD Release 0.0 ・ 386BSD Release 0.1 ・ 386BSD Release 1.0 ・ 386 の割り込み制御・ 3BSD ・ 4.2BSD ・ 4.3BSD ・ 4.3BSD Reno ・ 410 a. out ファイルフォーマット・ 413 a. out ファイルフォーマット・ 4BSD 68000 ・ ・・ 534 ・・ 180 ・・ 38 ・・ 37 ・・ 466 ・・ 535 ・・ 300 ・・ 471 ・・ 36 ・・ 38 ・・ 11 ・・ 11 , 49 ・・ 92 , 101 , 186 , 254 , ・・ 303 , 471 445 , 462 , 538 ・・ 36 ・・ 446 ・・ 446 ・・ 402 ・・ 101 ・・ 466 ・・ 466 ・・ 465 applications program interface ・ applications program interfaces ・・ APTmap ・・ argc ・ AST ・ ast ・ asynchronous trap ・ BerkeIey TimeSharing System ・ BIank Storage Segment ・ BIOS ・ biomask ・ bio ・ BerkeIey UNIX ・ call gate ・ BUS-ALIGN-TRAP ・ bss ・ BSD ・ BOUND ・ ・・ 104 , 112 , 163 , 257 , 300 , 359 80386 System Software Writers Guide ・ a. out ・ AIX ・ ALL ・ alloctss() ・ Alternate Page Table map ・ API ・ Apple ・ ・・ 63 ・・ 400 ・・ 389 ・・ 151 ・・ 48 ・・ 174 ・・ 273 , 442 canonical name ・ cansignal() ・ XXX ・ cfg-string() ・ cfg-skipwhite() ・ cfg-number() ・ cfg-namelist() ・ cfg-char() ・ cfg- Compaq Systempro ・・ closef() ・ close() ・ ・・ 304 , 305 , 320 , 321 575 ・・ 173 ・・ 172 ・・ 442 ・・ 28 ・・ 273 ・・ 40 , 48 ・・ 401 ・・ 484 ・ 190 ・・ 179 ・・ 195 ・・ 190 ・・ 194 ・・ 197 ・・ 196 ・・ 153 ・・ 203 ・ 122 ・・ 55 ・・ 121 ・・ 55 ・・ 101 ・・ 104 ・・ 12 ・ 12 ・・ 120 ・・ 120 ・・ 143 ・・ 459 ・・ 485 , 522 , 524 ・・ 49 , 454 , 460 ・・ 47 , 168 , 187
40 劭叩 r3 / 叩 the E れ ro れ襯 2 れた Me 肱 0 ホ The simple answer, Of course, is that life is priceless but that turns out tO be not very helpful. Because the resources used tO prevent IOSS Of life are scarce' choices must be made. The economic approach tO valuing lifesaving reductions in risk is tO calcu- late the change in the probability Of death resulting from the reduction in environmental risk and t0 place a value on the change. Thus, it is not life itself that is being valued but rather a reduction in the probability that some segment Of the population could be expected tO die ear- lier than otherwise. lt is possible t0 translate the value derived from this procedure in an "implied value Of human life. " This is accomplished bY dividing the amount each individual is willing t0 pay for a specific reduction in the probability 0f death bY the probability reduction. SUPPOS% for example, that a particular environmental POlicy could be expected tO reduce the average con- centration Of a toxic substance tO which one million people are exposed. SUPPOSe further that this reduction in exposure could be expected t0 reduce the risk 0f death from 1 out 0f 100 , 000 t0 1 out 0f 150 , 000. This implies that the number 0f expected deaths would fall from 10 t0 6.67 in the exposed population as a result Of this policy. If each Of the one million persons exposed is willing t0 pay $ 5 for this risk reduction (for a total 0f $ 5 million)' then the implied value of a life is approximately $ 1.5 million ( $ 5 million divided bY ー 3.33 レ What actual values have been denve from these methods? A survey (Viscusi, 1996 ) 0f a large number 0f studies examining reductions in a number Of life-threatening risks found that most implied values for human life ()n 1986 dollars) were between $ 3 million and $ 7 mil- lion. This same survey went on tO suggest that the most 叩 propriate estimates were probably closer tO the $ 5 million estimate. ln Other words, all government programs resulting in risk reductions costing less than $ 5 million would be justified in benefit-cost terms. Those costing more might or might not be justified, depending on the appropriate value 0f a life saved in the particular risk context being examined. HOW have health, safety and environmental regulations lived up t0 this recommendation? TabIe 3.2 suggests, not very well. A very large number 0f regulations listed in that table could be justified only if the value 0f a life saved were much higher than the upper value 0f $ 7 million. lssues ⅲ Benefit Es 黼 m 黼 0n3 The analyst charged with the responsibility for performing a benefit-cost analysis encounters many decision POints requiring judgment. If we are tO understand benefit-cost analysis, the nature Of these judgments must be clear in our minds. Primary Versus Secondary Effects. Environmental projects usually trigger b0th primary and secondary consequences. For example, the primary effect Of cleaning a lake will be an increase in recreational uses Of the lake. This primary effect will cause a further ripple effect on services provided tO the increased number 0f users Of the lake. Are these secondary benefits tO be counted? The answer depends upon the employment conditions in the surrounding area. If this increase in demand results in employment Of previously unused resources, such as labor, the 3This section relies heavily on Peskin, Henry M. and Eugene Seskin, CO 豆 - B 例 e れ記彑 s なイⅢ e た PO ″われ Co れ〃 0 / 物″ c. 彑 (Washington, D ℃ . : The Urban lnstitute, 1975 ).
348 C ん叩 r 77 Ⅳ催 PO ″われ cEx MARKETABLE EMISSION PERMITS 0N THE FOX RIVER を With the advent of the bubble and offset policies, marketable emission permits have become the centerpiece Of the regulatory reform movement in air pollution control. Though no compa- rable scale 0f reform exists for control 0f water pollution, one attempt has been initiated in northern Wisconsin. The Lower Fox River flows from Lake Winnebago t0 Green Bay, Wisconsin. Lining the banks of a key 22-mile segment 0f this river are 10 pulp and P 叩 er mills and 4 municipalities that discharge effluent intO the river. During the summer the desired DO targets are not reached at tW0 critical sag points, even when the industrial polluters are in compliance with BPT stan- dards and the municipal polluters are providing secondary treatment. The Wisconsin Department of Natural Resources was faced with meeting the standards in the face Of industrial resistance. TO assist in choosing a policy strategy, it funded a simulation model Of the river tO compare traditionalregulatory rules with a marketable-permit system. This model revealed significant differences among dischargers, a precondition if the market 叩 proach is t0 reach the environmental goals at a significantly lower cost. Under traditional abate- ment rules, marginal abatement costs differed by a factor 0f 4. The study concluded that the con- trol costs would be some 40 percent higher if the department were t0 rely on traditional abatement rules. The potential annual saving realized from a permit approach was estimated at $ 6.7 million. ln March 1981 the department approved regulations allowing dischargers on the Lower Fox River to transfer permits by approved contracts. By 1982 the first trade had already taken place, but that also proved t0 be the only trade prior t0 1990. The system clearly has not lived up tO expectations, an experience that probably will inhibit any expansion Of the concept t0 Othe r geographi c areas. Source: This example was drawn from William B. O'Neill, "P011ution Permits, and Markets for Water QualitY," an unpublished Ph. D. dissertation completed at the University ofWisconsin—Madison, 1980 , and subsequent conversations with the author. discharge level. The charge is waived for three years prior t0 the installation Of new pollution control equipment promising further reductions Of at least 20 percent. Revenues from the charges can be used by the administering authorities for covering administrative costs and for financial assistance tO public and private pollution-abatement activities. Though these European approaches differ from one to another and are not all cost effec- tive, their existence suggests that effluent charge systems are possible and practical. The Ger- man Council Of Experts on EnvironmentaI Questions estimated the German effluent charge policy tO be about one-third cheaper for the polluters as a group than an otherwise compara- ble uniform treatment policy. Furthermore, the policy encouraged firms to go beyond the uniform standards when the cost Of such effort was justified.
The ルロ矼 To c S ″房れ ce Po 朝れ 381 as pesticides, are tOXiC by design. Yet, in excess concentrations, even a benign substance such as table salt can be toxic. A degree Of risk is involved when using any chemical substance. There are benefits as well. The task for public policy is to define an acceptable risk by balancing the costs and bene- fits of controlling the use of chemical substances. Health Effects The two main health concerns associated with toxic substances are ( 1 ) risk of cancer and ( 2 ) effects on reproduction. Since the 1900S , mortality rates have fallen for most of the major causes of Cancer. death. The most conspicuous exception is cancer. Even the mortality rate for heart disease, the number one killer, has declined in recent decades. Meanwhile, the mortality rate for cancer, currently the second most common cause Of death, has increased steadily through this century. Although many suspect that this increased mortality rate for cancer may be related to increased exposure tO carcinogens, proving or disproving thiS link iS very difficult because Of the 例 cy of the disease. ln this context, latency refers to the state of being concealed during the periOd between exposure tO the carcinogen and the detection Of cancer. Latency periods for cancer can run from 15 t0 40 years in length, but have been known t0 run as long as 75 years. 2 ln the United States, part of the increase in cancer has been convincingly linked to smoking, particularly among women. The proportion Of women whO smoke has increased, and the incidence of lung cancer has increased as well. Smoking does not account for all of the increase in cancer, however. A smaller percentage Of men smoke tOday than in earlier decades, and modern cigarettes contain less tar. Despite this, the incidence Of lung cancer among men has increased. 3 Though it is not entirely clear what other agents may be responsible, one cause that has been suggested is the rise in the manufacture and use 0f synthetic chemicals since World War Ⅱ .4 A number of these chemicals have been shown in the laboratory to be carcinogenic. That does not necessarily implicate them in the rise of cancer, however, because it does not take exposure intO account. The laboratory can reveal, through animal tests, the relationship between dosage and resulting effects. TO track down the significance Of any chemical in causing cancer in the general population would require an estimate Of hOW large a segment Of the population was exposed tO various doses. Currently, our data are not extensive enough to allow these kinds 0f calculations t0 be done with any confidence. 2Paul R. Portney, "Toxic Substance PoIicy and the Protection of Human HeaIth, ” in C ″″ e お s ″加し & Environ- m 例 / 記 PO ″ c. 彑 , Paul R. Portney, ed. (Baltimore, MD: J0hns H 叩 kins University Press, 1978 ) : 100. 3CounciI on Environmental Quality, E れ ro れ襯 I Q ″記″ーー 7980 (Washington, DC: Government Printing Office, 1980 ) : 194. 4Davis and Magee raise this possibility but 引 SO conclude that, because Of the latency period, it is tOO early tO tell hOW much, if any, Of the responsibility can be assigned tO the increased exposure tO synthetic chemicals. See Devra Lee Davis and Brian H. Magee, "Cancer and lndustrial Chemical Production," Sc たれ 206 ( 21 December 1979 ) : 1356 ー 1358.
50 GREAT B A N T A M C L A S S I C Edited by Milton Crane SHORT STORIES
428 劭叩 r 20 D ツ 0 〃襯 P 側催 , and the E れれ襯 e overproduction. Overvalued exchange rates increase the attractiveness Of importing fOOd and decrease the attractiveness Of exporting f00d. By discouraging small-scale agriculture in developing countries an activity that would provide income tO a segment Of the population faced with the most severe forms Of povertY' biased trade flOWS exacerbate the poverty problem. because income increases targeted on this particular group typically lead tO slower population growth' even some Of the population pressures on the environment could ultimately be related tO biases in current trade patterns. One common stereotype Of the difference between developed and less-developed countries involves their respective supplies Of minerals. According tO this stereotype, less-developed countries control most Of the world's mineral resources, and the developed world creates the demand for them. If accurate, this view would suggest that rising mineral prices would even- tually create favorable terms Of trade for most developing countries. Unfortunately, upon closer inspection this stereotype represents, at best, an oversimplifi- cation. Although exports Of minerals have increased from less developed t0 developed coun- tries, not all less developed countries share these higher export levels. A few have large reserves Of petroleum or nonfuel minerals, but most dO not. The benefits from increasing mineral prices tend tO bypass most less developed countries. Debt. Many third-world countries have staggering levels 0f debt t0 service. The World Bank has estimated that the total external debt 0f all developing countries reached $ 2 trillion in 1997. ln 1989 poor nations sent $ 51.6 billion more to the industrialized nations in interest and principal repayment than they received in new capital. 28 External debt in 1997 was 92.3 percent Of the gross national product Of the severely indebted low-income countries. These percentages reach as high as 236.0 percent for Guyana and 305.6 percent for Nicaragua. 29 Unfortunately, even private capital is flowing out Of the capital-poor countries, where it is desperately needed, and intO the c 叩 ital-rich countries. The World Bank estimates that the stock 0f "flight ” capital held abroad by citizens 0f severely indebted countries equals a signifi- cant fraction Of those countries' external debt. ln periods Of high real interest rates, servicing these debts puts a significant drain on for- eign exchange Of earnings. Using these foreign exchange earnings tO service the debt elimi- nates the possibility Of using them tO finance imports for sustainable activities tO alleviate poverty. One study found that, in all but one Of the most indebted countries, the rati0 Of invest- ment t0 GDP was substantially lower in the 1982 ー 1988 period (when the debt burden was heaviest) than in the previous six years. 30 ln Argentina the ratiO fell from 25 percent tO 15 per- cent, whereas comparable figures for Venezuela indicate a fall from 33 percent tO 18 percent. This fall in investment has, in turn, reduced the growth of output and exports in debtor nations and, thereby, further undermined their ability t0 repay their debts. 28Even if a11 official development assistance and private c 叩 ital flows to the developing countries were included in the total, the net outflow would still be $ 9.8 billion. This evidence on the debt comes from the World Bank, Ⅳ Debt 7989 ー 90 , 物ん襯 e ノ (Washington, DC: World Bank, 1989 ) : 1 ー 9. 29United Nations, 〃″襯 D el 叩襯例ー印 0 99 (New York: Oxford Press). 30"Debtors' Hangover, ” The Eco れ 0 襯な日 20 May 1989 ) : 73.
Pre-Quiz ・ Choose the answer you think is best. 1 Which of these plays a key role in photosynthesis? a. Venus b. Fertilizer c. The Sun 2 . What ro 厄 do human beings play in a food chain? a. The 「 0 of decomposers b. The ro 厄 of producers C. The 「 0 Of consumers 3 . HOW dO you describe an animalif its species has been wiped out? a. Polished b. Extinct c. Endangered 4 . Which of these is a producer? a. A zebra b. A fungus c. A pine tree 5 . What do you call an animal that eats both plants and meat? a. A carnivore b. A herbivore C. An omnivore 220