begin {< l¢nh_tl/(ll1_W >} end [< ten JhJ((/!1ti_fn'llhJol1 >1; Vi dy sau day eho fa thay ma tti ella th,1n chuang trlnh con. Chu y rang. khi g9i ham function, phcp gqi ham se b! ng.it khi thl!c hi~n den cflu l~nh return. Cau l~nh return xac dinh gia tfi tra l<;ti cho phep g9i chuang Trinh can. Vi ely, Funtion lncrementer ( Count: integer) return integer is variable Temp: intcger ; bcgin if ( Count >= 255 ) then Temp :=0; else Temp := Count + 1 ; end ir; return ( Tcmp ); end Incrementer; Khi g9i chuang Trinh can, cac doi luqng thl!c te wang u-ng voi tham so hlnh thue lop variable pMi la eac hien; wang u-ng voi lop constant phai la hang so ho~c bieu thuc va tu{mg ung voi lOp signal phai Iil tin hi~u. Ok hang so va bien duq'c truy~n thea gia tr!, con tin hi~u duq'c truy~n thea dja chi. Do do doi voi lOp doi tlIq'ng tin hi~u thl mQi tae d¢ng len tham so truyen vao than chuang Trinh can cling chinh Iii tac d¢ng (fI!C tiep len tin hi~u dUQ'c truyen vao. Chung ta hay xet vi d1,l chuang Trinh con sau: 198 Vi d~l, procedure Send ( signal CLK: BIT ; Data: integer; begin signal Ack: BIT; signal Ready: out BIT; signal Wire: out integer) is wait until ( CLK'event and CLK = '1' and Ack = '1" ); wire <= Data; Ready <= '1 '; wait until (elK'evcnt and eLK = 'I' and Ack ~'l' ): Ready <= '0'; cnd Send; 2. Cae ham quyet d~nh Cluing ta bittt d.ng, moi tIn hit?u deu XUilt piull ttl mt)1 n,gu(lIl. ,'\l6i each kiuic la moi lill hj~u c6 mc)t di~u khi~n. Trong nhi~u truang ILl/p. VI dl,! nlm khi cae duang tIn hi¢u bi ch(lp l~L tin hi¢u eli ra kh6i nut ch~lp ~C du'<,1c H~ng hqp ttl cae tin hi¢u di V~IO nut theo m(H iu~t xac dinh. Trang trliang hqp nilY, chung la noi rang 1111 hi¢u di fa khoi nUt eh~p co nhi~u ditu khi6n. Ng.6n I1gfr YHDL cho plH~p chung ta c6 th~ xic dinh ca.c lin hi~u xuii! phat Ill' nhieu nguon neu su- dl,log nhung ham quyel djnh. Nhung ham quyct dinh nilY dung de xic dinh gia tI"! cua duo-ng tin hi¢u tll nhilng gia trj nh~n duqc III nhi~u nguon dicu khi6n. Y i dl,!, Qua trinh i Tin hieu Ham quyet dinh Tin hll3U ( Q""ieh k Qua trinh j Tin hieu Tin hi$u lIinh 6.13. Sd do hallh vi clla cae qua trlnh sinh ra tin hieu co nhicu dieu khie'n. Trong vi dy. nay, d. hai qua trlnh process i va prol·l:.~. j cung di~u khi~n mt)t tin hi¢u, do do chung ta can c6 ham quyet dinh dt xae djnh giri tr! cho tfn hi¢u nhi.~n dlI,!C. Doi voi qua Idnh mo phong, cae ham guyet dinh (.;0.) the ,,' mQi ham bao gum cae cbuang trlnh viel tren ngon ngil YHDL. Trang nhLrng m~ch thtJc. ket qua el\a cae ham quyet d~nh la lien ket cae tin hi¢u va cung cho qua lTI¢t phan tu logic d~c bi¢t c6 m¢t dau Ca. Trang ky thu~t: chi co m¢t so gi{ji hqn 199 cae Trong cae phall eUng chi c6 mQt vai ki~u thl,Ic hi¢n cae ham quyct r.1jnh nhl1 lien ket d~ng Or, lien ket d,-~ng And ho~e lien ket d~ng ba tr~ng thii ( hinh 6.14). Lien ket d~ng Or Lien ket d,~mg And Sa tr~ng thai Uinh 6.14. Cac bieu (lien phan tung Clla de hinn quyct d!nh: harn quyc't dinh d,!-ng Or. dang And viI ba trang IIia1. Cac tin hi¢u dugc cac ham quyet dinh t<~o ra neu khai bao cua tin hi~u chua d cac ham quyet dinh ho<!-c khai bao ki~u can eua tin hi~u chua h~l.In quyet djnh. Vi dy, signal NODE: WIRE_AND BIT: subtype RESOLVED_STD is WIRE_OR STD_ULOGIC: Trang vi dy nay, khai bao thu nh[\t cho chung ta lhay tin hi¢u NODE la tin hi~u dugc xae dinh \'6i ham quyct dinh la WIRE_AND. Moi khi xual hi~n sl,I ki~n tren duang tin hi¢u NODE, ham WIRE_AND duqc gQi va tnt li.li gia II"! ki~u BIT - l.1 gia trj cua t[n hi¢u NODE. Khai baa thu hai xae djnh kit!u con duqc quyet dinh RESOLVED_STD. C<ic tin hi¢u dW1C khai bao thuQc ki~u RESOLVED_STD Itt nhung tin hi¢u dU'qc quyet dinh. Duai day chung ta thay each de x<ic dinh va sir dl:mg dc tin hi¢u duqc quyet djnh: - Xac dtnh ki~u tin hi¢u ( neu can thiet ): - Xac djnh ham quyet dinh. Ham nay sc nh~n cac lin hiGu vao va tra I'!.i tin hi¢u thuQe kieu dii dUQ'e xae dinh; - Khai baa kieu con cua ki~u tin hi~u kern v6i ham quyet djnh; - Khai bio va Slr dt:lI1g cac tin hi¢u dugc quyct djnh. Trong vi dt,l dttai day. chung ta thay tin hi~u Z dttCJe khai bao Itt thuQc ki~u dttqc quyet d!nh WIREOR_STD, trong d6 h~l.ln quyct d!nh cua kitu tin hi¢u la WIRE_OR. Trong kien true, chung ta co hai phep gan tin hi¢u dong thoi. Cii hai phep gan deu gan gia trj cho tin hi¢u Z. Nhtt v~y tin hi9u Z se nMn 200 gia tr\ dl1qc x<ic d,nh qua phep lOan or giil:a hai dau vao cua ham quyet djnh: ( [j and 12 ) vii ( 13 xor 14 ). Vi dl,l. architecture Resolved ArchofWOR is begin runction WIRE_OR( Din: in STD_UU1GIC VECroR ) return STD_ULOGIC is begin return( Din( 0 ) or Din( 1 »; end WIRLOR; subtype WIREOR_STD is WIRE_OR STD_ULOGIC; signal II, 12, 13, 14: STD_ULOGlC; signal Z: WlREOR_STD; Z <= II and 12; 7. <= 13 xor 14; end WOR; Cac goi chuang trlnh STD_LOGIC_1164 cua tim vi~n IEEE chua cae kieu dl1 li¢u duqc quyct o,nh la SID_LOGIC va STD_LOGIC_ VECIOR. D<~ng quyc"t d(nh cua kitu STD_LOGTC lit d<;lng quyet ujnh thea ba tn~ng thai. Cae tin hi¢u co nhieu nguon uleu khitn se duC}c gan eho tin hi¢u -kitu STD _LOGIC V~l gia tri duqc quyct d(nh boi cae ham ba tr<;tng thai. 3. Cac g6i ChUling trinh Cac kitu dil: li¢u, hang s6 va chuang trlnh can co the: duqc khai hao ben ~ck~~o~~~~t~_c~ck~~.Qc~ baa nay ta cl,lc b~ nang nhil:ng kien truc wong ung va thlfc thc' kluic kh6ng the truy e~p t6i nhung doi tuqng do. Tuy nhlen traog nhi~u truong hqp nhung kie"o truc khac nhau cung co the phai chia sf: nhung doi tuqng chung nao do. Gic goi chuong trlnh ( Package,> ) trang ngoo ngu VHDL eho phep cluing ta thl!c hi~ll cae khai baa chung :ho nhicu thlfc tM khac nhau. MQt goi chuong trinh eua ngon ngu VHDL dugc biofu uien thanh hai phan: ph~n khai baa goi va than cua goi. 201 Phan khai hao goi m6 ta cae giao di-<?n cua goi va co cau true eu ph{Lp nhl1 sau, package < /('IlJ/la_g/ji > is {< cdc_ khm _ h(l() _lltl/O( WJ/ > I end [< lell_g6i >J; Cae khai b,lo ti1U¢e g6i co th~ la cae : Khai bao ki~u, kitu con, tin hi¢u, h,ing, bi¢t Janh: Khai bao thanh phan, chuang trlnh can; Lu(tt use: Va c6 the ehCra d de package khae. Otc kiwi bao tin hi~u trong g6i t~o ntn m<)t so van d~ trang qua trinh tong hqp m~lCh b6i \'1 Ill¢t tin hi~u kh6ng th~ philn phoi giO'a hai thl!C the. Cl.ch giai quyet thong d\lng van de nay la tin hi¢u sf: dL!(l'C khai baa nhu l11<)t tin hi¢u cuc h9. Noi each kh,ic, neu hai thl!C the SLr dl;!ng cung m<)t tin hi~u lrong gol, moi thl!C the sc nh~n duqc mOt phicn bun sao chep CLIa tin hi~u nay. Vi dl;! \'6 khai bao goi: library IEEE use IEEE.NUMERIC_IJITaU; package Watch_Pkg is subtype Mouth_type is interger range 0 to 12; subtype Date_type is intergcr range 0 to 3 !: subtype BCD4_type is unsigned ( 3 down to 0 ); subtype BCDS_type is unsigned ( 4 downto 0 ); constant BCDS_I: BCDS_lype :~ B"O_OOOI "; constant BCDS_7: RCDS_lype :~ B"O_OOOI "; function .BCD_Inc ( L : in BCD4_type) return BCD.'i_type: end Watch_Pkg: Than clla l11¢t g6i xac djnh dc h~ll1h vi cua g6i. Than cua mQt g6i iu6n ph,ij cung len voi khai h,}o goi. Phan than g6i duqc hat d,lU b6i Ill: khoa package body. Cae thong tin trong trong thin cua goi kh6ng th~ nhin th,iy 202 <luqe tu cae thiet ke' ho~e tlwe the sir dl;lng goi do. Nhu v~y IU cac thiet ke va eae thvc the chung la chi co the truy c~p tai cac d6i lUang trong g6i thong qua cae giao di¢n duqc xUc <l!nh trang philn khai bao g6i ma khong the' can thi¢p trvc tiep vao ben trung goi. Noi mQt dch kh;k goi hi. mQt hQp den vai cae giao di¢n <luqc dUa ra trung phan khai bao. Than cua goi duqc 1116 tii thea quy tic cu phap nhu sau: package body < len nla g/n > is { < cacJhm _/)(10 _tl ollg_t}uln grJ/ >} end [< thl_CJ/(lj;6i >J; Trang phan khai bao trong than goi co th~ chua eac: Khai ban kieu, kie'u con, h~ng; - Than ehuOllg t lnh can; - ~u~t usc. Vi dl,! <luai day cho chung la thay vi~c m6 tii than cua goi trang ngon ngu VHDL: package body W A TCH]KG is function BCD_INC ( L: in BCD4_ TYPE) return RCDS_ TYPE is variable VI, V2, V: BCDS_TYPE: begin V I := L + BCD5 - I : V2 := L + BCD5 - 7 , case V2( 4 ) is when '0' => V:= VI; when 'J' => V := V2; end case; return ( V ); end BCD_INC, end WATCH_PKG, Cae phdn tu duqc m6 ta trang pha.n khai bao g6i kh6ng the nhln IhAy duqc mQt each tv dQllg tu cac thu \'i~n khac. Lu~t usc dung tmae mQI dan \"! chuang tdnh se lam cho lal ca cac pl,3n tu trang phil.Il khai hi.lO goi e6 the' dUQ'c lruy Ci)p tu dan vj chuang trlnh d6. Vi dl,!, gi;i thiet rang, goi chuong 20] ldnh WATCH_PKG neu tren dUCK bien dich va dua vao thu vi9n MY_LIBRARY. De: co the: si'r dl,lng cac khai bao trong goi WATCH_PKG, chung ta can dua chung vao thu vi¢n chuang tdnh hi~n Ihai SLr dl,lng dot~n l~nh sau: library MY_LIBRARY; lISC MY_LIBRARY. WATCH]KG.all; HQi dong ChLl<1n hoa IEEE xac djnh hai thu vi¢n cho ngon ngi1 VHDL ia STD va IEEE. Moi thu vi¢n chua rnQt so goi nhu: STANDARD va TEXTIO doi vai thL( vi¢n STD. Goi STANDARD xac djnh cac kieu du li~u quan tn?ng nhu integer, boolean, BIT STD_LOGICI164, NUMERIC_BIT, NUMERICSTD doi ,oi Ihu vi¢n IEEE. Cac goi nay chua cac kie:u va nhfrng haITI quan tr",ng eha qua trinh tcing hqp va rnb phong bang ngbn ngiJ VHDL Trong chuang nay c1lling ta d1t khao sat nhung d~c die:m co ban eua ngbn ngu VHDL - lTI¢t ngon ngu rno ta ph<1n cling dien hloh. Ngon ngu- nay dUQ'c dung de: 1110 hinh hoa m~ch trong cbng ngh¢ thiet ke, ehe h.\O l11<;lch voi d¢ tich h0P eao va sieu cuo. Nhilng Ihinh phan chfnh eua ngon ngil nhu cac l¢nh tu.}n IL!, cae l¢nh song song, cUc chuang tdnh con, cac phu"Cing pluip 1116 tA thL!C the va phuong phap lu~n bicu dien l11<;tch theo cau chue, hanh vi hO~lC theo dong dfr li¢u drr dUQ'C de c~p t6i. Trong chuang tiep theo chung ta <;Lr d'-:lng ngbn ngil VHDL de Xi)Y d~rng dc mb hinh nhilng In' lch logic cel ban. ' 204 . Tcmp ); end Incrementer; Khi g9i chuang Trinh can, cac doi luqng thl!c te wang u-ng voi tham so hlnh thue lop variable pMi la eac hien; wang u-ng voi lop constant phai la hang. thu~t: chi co m¢t so gi{ji hqn 199 cae Trong cae phall eUng chi c6 mQt vai ki~u thl,Ic hi¢n cae ham quyct r.1jnh nhl1 lien ket d~ng Or, lien ket d ,-~ ng And ho~e lien ket d~ng. djnh: - Xac dtnh ki~u tin hi¢u ( neu can thiet ): - Xac djnh ham quyet dinh. Ham nay sc nh~n cac lin hiGu vao va tra I'!.i tin hi¢u thuQe kieu dii dUQ'e xae dinh; -