Trang vi dl,l nay, tin hi¢u S duqe e~p nh~t 10 Ian trong vang l(tp. Hanh vi n~ty se khong duqe b(> mo phung th~ hi¢n. Tuy nhien, cae ket 4u;i tue thoi co the dUQ'C hi~n thi lrang qua Idnh !TI6 phung ke't qua tdng hqp mi leh. 7. Call I~nh next L¢nh next chi dung trong cae vong l~p. L¢nh nay co tae d~ng lo"~1 bo vi~c thl!e hi¢n uk c;.tU lc;nh nam giUa eau l~nh next va cuoi vong h)p khi dieu ki¢n lrong can l¢nh duqc nghi¢m dung ( tuang tl.r l¢nh continue trong ngon ngfr C ). L¢nh next co eftU truc cu phap nhu Si.lU, next [< nhiin _w)ng_/(lp >][ when < di/I1_ ki¢n > L Trang twang hqp co dc Yang l~p lOng nhau thl vi¢c th!!c hi~n l¢nh next sc duqc xac d~nh mQt cach tuong rninh htmg < nhilll_\"(Jng_'{/jJ >. Neu khong c6 nhLin vlmg 1~IP trong c<tU l¢nh. lc;nh next se lac dy.ng len vong I~p trong cling chua l¢nh next. Vf dl!, L I : while I < 10 loup L2: while J < 10 loop next Ll when I = .I; end loop L2; end loop L1; 8. Cau I~nh exit Cau l¢nh exit co tht duqc dung ben trang cae \'oog "JP. CflU J¢nh nay e6 t[le dl,lng b6 4ua cae l¢nh con !i li cua vong l(tp va th!!c hi~n ngay J¢nh tiep sau vong I~p vua ket thuc. L¢nh exit e6 clu true Cll phap nhu sau, exit [< J/J/(JI1_l'img_l(ip >][ when < Ji["u_ ki(;/1 >]; 9. Call I~nh wait L¢nh wait dieu khien bl) 1116 phong ngilng vi¢e tlwc hi¢n cae qUi.i trlnh hO(lc cae chuffilg I["lnh con eho 16i khi dicu ki~n ben trang cau l~nh duCjc 184 nghi~rn dung. Ta co the noi dlng dieu ki~n trong diu l~nh wait chi co the duqc nghi~rn dung khi XU[lt hi~n cae sl! ki~n tren dl1ang tin hi~tl. Nhu \'~y. Ulc doi tl1qng di11i~u tham gia trong trung dieu ki¢n phui HI cae tin hicu. etc dieu kiGI1 de ti~p wc qua trinh bt dung co the duqc bicu thj duai ba d' mg sau day trung ngon ngQ VHDL: wait [on < {(ill {/II 111('/1 > \' < {ell fill IIh'JI > \ J - - . - - . l until < hilill tM(c fo,<ic >] - - < [for < bi/lI_flufc_tllrfi_MiulI >1; Gill l¢nh wait on: chi cho chung 1a danh stich dc duang tin hi¢u ma b(l mo phong sc cila sl! ki~n ( sl! lhay d6i tr~ng thai cae lill hi¢u ). Vi dl.l, doi voi cau l¢nh wait on A.B; qua trinh rna ph6ng sc dUng l<;li eho den khi c6 xuat hi~n sl! ki~n tren dUOng tin hi~u A, hO(lc B. Sau do b(l rna ph6ng se tiep Il,lC thl!c hi¢n C[IU l¢nh dung sau \¢nh wait. Cfm l~nh wait until sc dil'tlg vi¢c thl!c hi¢n qu,i tdnh cho tai khi bi~u th(~c logic nh~n gill trj truc. GIU I~nh wait Im.li nay se t~lO ra mQt danh saeh ng,im dinh dc tin hi9U lac dOng trong bitu lh(rc logic. Moi kili co h[it ky mQt Sl! ki~n xu[i't hi¢n tren duang tin hi¢u trong danh sach n~ly, bieu lillIe 16gic se dm.K tlnh. Trong twang hgp l¢nh wait until khong chua bieu thuc l6gic, chung ta hieu rtlllg cau l~nh se la wait until truc. Vi dl,l Slr dl,lllg l¢nh wait until, wait until x < 10; qua t["lnll tlwc hi¢n se dung l~i cho tai khi x < 10. Cau l¢nh wait for se dung vi~c rn6 ph6ng qUit trlnh m()t thai gian bAng gia tri thai gi,m duqc chi djnh ben trong dieu ki~n. Sau khoang thai giun duqc chi dinh, h9 rno phong thl!c hi¢n I¢nh tic'p theo sau l¢nh wait. Neu bitu thue thai gian khong co, chung ta hitu ding l¢nh wait c6 y nghia nhu sau: wait for time'high; 185 dieu nay co nghIa HI. chung ta kh6ng co chi dinh wang minh ve thoi gian eho, Vi dl,l ve Slr dl,lng cau I¢nh wait for, wait for IOns; Cac hla chQn tren co th6 duqc Slr dyng dong thai. nhu tcong vi dy duui day: wait on A, B until ( x < 10 ) for 10 ns; diell nay co nghIa la b¢ m6 phong se eho khi c6 thay doi tin hi¢ll A hO(lC B va se tiep tyc chi khi ( x < 10 ) t(!.i thoi di~m xufit hi¢n sy' ki¢n, ho<!.c eho toi khi 10 ns da troi qua. Trong qua tclnh m6 hinh hoa Im,lch, l¢nh wait co tht' dtrqc dung t1e thief J(tp dong ho cho che d¢ dong b(>, Trong cac rna hinh thiet k6 bang ngan ngfr VHDL. J¢oh wait ogling qua tdnh thl!C hi~n cho lui xuat hi¢n suiYn dutmg ho~c suiJn am lren duemg tin hi¢u. Vi dy, khi rna hinh hoa phan tir triga D lam vi¢c trang che d¢ dong b¢ thea suan duong, chung ta co the' nh(tn thrqc dm,lI1 chuong tdnh VHDL nhu sau. entity D_FF is port (eLK: in BIT; D: in BIT; Q: bulTer BIT); end D_FF; architecture Behavior of D_FF is begin process wait until CLK'evcnt and CLK = ' 1 '; Q<~D; end process; end Behavior; 10. Phcp gl)i chuang trinh con va I~nh return Trong ngan ngiJ VHDL co hai d~ng chuang trinh con: 186 Thu tl,lc: procedure co th~ tni.l:;ti nhieu gia trj: Ha111: function chi tnt l~i mQt gia trj va co th6 tham gia vao cae bi{;u thue. Cau l¢nh return dung de ket thlic hO<;l.1 dQng eua cae clllrtmg tdnh can va chi duqe Slr dl.mg trang h~un hO~IC thu tL,lc. D6i voj ham, Sl.1 co m,~t eua l~nh return la bal bu()e con trong thu tL,lC thl khong bat huge. L¢nh return co diu truc eu phap Bhu sau: §6.6. Cac call true song song Trong ngon ngu VHDL, 1119t kicn true c6 the ehua m¢t ha~c nhieu ci.k eau true song song. Moi eau trlie song song xae dinh Jl1~)t Jon vi tinh toan baa gom cae thaa tae JQe tin hi¢u, thl,l'e hi¢tl eae tinh tmin \r~n cae gia tr~ tin hi~u va gan nhung gia Iri tlnh dLIqc eho tin hi~u ra. Cac cau true song song xae dinh cae thanh philn va cae qua tdoh lien ket nhung thilnh phan d6 bttng nhilng cau true va hanh vi eua cae thl;Ic the. Cie diu true song song se duqe thl;Ie hi~n dong thai trong qua trlnh mo phong khong pJW thU(lC VtlO Ir(l\ II! xuat hi¢n eua chung Irong kien true. Trong ngon ngu YHDL e6 cae eau true song song sau: Qua trlnh process; Cae phcp grin tin hi¢u song song; Phcp gan tin hi¢u eo dieu ki~n; Phcp gan tin hi¢u eo Jl!a eh(:m; Khoi; Phep gQi chuang tdnh con song song. 1. Cac qua trinh process Qua trlnh tinh loan process duqe 1<).0 thanh tll m()1 li!-p hqp cae cuu l¢nh tufin II!. Tal d cae qua trlnh process Iml1g 111(H Ihicl ke duqe Illlfc hi¢n m91 each song song. Tuy v~y, t;:ti 1119t thai diem xae djnh chi co 111¢1 cau I¢nh 187 tuAn tt! dUQ"c tlwc hi¢n trong moi qua trlnh process. M<.)I quit tflnh process lien kct voi phan eon h.ll eua thlet ke' thong qua cae thao tac dc:)C ciie giil trj tit dc tin hi¢u d:iu \'iI0, cUc c6ng dU"9"e khai bao ngoili qUii lrlnh ho(1C ghi gia tri vito eac tin hi¢u, cong 06. M¢t qua trlnh t[nh toan process dUQ"c rn6 Iii theo quy tac cu phiip sau: [< 11/1(/11 >:] proccss [« donI! sdch ctic tin hi~;11 {(Ie J()J/g >)) 1< pll(lllJlwi_lhlo > I bq!;in 1< /11111 _tllclll_/l/ > J end process [< I1hiln >]; < pll(ln Jlwi _btio > oinh nghia cac doi tlIQ"ng ton {<.Ii el,le b6 Hung process ban gom: - Cac khai ban bien, khai baa hang, khai baa kitu, kieu eon; - Than chvang trlnh can, khai baa cae bi~t danh. lu~t use. Neu qua trinh chua < d(JII"_s(irll_c6c_lfl1_hi~;/{_tdc_J(Jl1g > thi ILk 06 qua trinh nay se tuang ttf nhv qua trinh kh6ng chua danh sueh tin hi¢u tac d¢ng nhung li;li chua l¢nh wait a v~ tri cau I¢nh cuoi cling trong qua trlnh: wait on < dal1it _"'rlch _ c(/c_till_hi¢ll_t(lc_d()/lg >; Nhung qua trinh d6 kh6ng can c6 sl! xuat hi¢n tuang minh eua I¢nh wait. Vi¢c thvc hi¢n mqt qua trlnh proccss baa g6m vi¢c thtfc hi¢n l~p h.ll dc c[iu true wan ttf eilIIa ben trang than qua trinh. Sau khi c,lu l¢nh tu,1n ttf cu6i cling dugc tht!c hi~n, \'i¢c md ph6ng qua trlnh se dUQ'c bAt dau I\li tll C[IU l¢nh twin tl,f dau tien eua qua trlnh. Dieu nay lam cha vi~e 1116 ph6ng hm.it d(mg cua qua trlnh giong nhll Ill')t vong Iij.p vo hi 1ll baa g()m tat d cac du l¢nh tWIn tV bcn trong qua trinh. Vi¢e thtfc hi~n m6 phong qua trinh process e6 the bi dung Ii.li bang Cil.U l¢nh wait va co th6 dl1gc kich ho;;tlI;;ti khi xu[it hi¢n sl! ki¢n trcn cac duang tin hi~u trong danh such tIn hi¢u hic o¢ng. Chung ta hay xet vi dl,l mb r,lnh hoa b') ma hoa 8~3. Qua trlnh bi6u oien b¢ ma hoa nay se c6 danh sach tin hi~u tac d¢ng g6m cae tin hi¢u y I, y2, y3, y4, y5, y6, y7, Dicu nay eGng lUang duang voi m<.)t qua trl11h khong c6 oanh sach tfn hi~u tac d¢llg nhung chua cau l¢nh: 188 wait on y I. y2, )'3, y4, yS. y6, y7; t<.li V! trl cftu I¢nh cuoi cimg trang 4U;'\' trlnh. BQ ma haa 8 -> 3 duqc 111(1 t,'l bang dm.1l1 ehu'ong trlnh VHDL duai day: entity Encoder is port (yl. y2, y3. y4, yS, y6, y7: in BIT; Vec: out BI1''-VECTOR ( 2 downto 0)); ('nd Encoder; architecture Behavior of Encoder is hq!;in process( y I, y2, y3, y4. y5. y6. )'7) begin if( y7 ~ '1') then Vee <~ "III"; clsif"( y6 ~'I' ) then Vee <~ "110": elsif ( y5 = '1' ) then V cc <= " JO 1 "; elsif ( y4 = '1' ) then Vee <= "100"; elsif( y3 = '1') then Vec <= "all "; elsif( y2 = 'I') then Vee <= "010"; elsif( )'"1 = 'I') then Vee <= "001"; else Vee <= "000"; end if; end prol'css; end Bcha\'ior; Chung ta xct 111Qt VI d~ ve 51! tuang tac giua hai qua trinh. d dfly chung ta co Il1Qt qua trtnh gt'ri thong tin va qm!. tr"inh thu hai nh(lll thong tin. Qm\. trlnh glfi thdng lin co danh soiell tin hi¢u tae dQng g6m hai tin hi¢u CLK \,~l Ack. Qu.i trlnh nh(Ul e6 hai tin hi¢u trong danh sach tin hi¢u lac dC)ng eLK V~l Ready. Hai qua trinh nilY dong b(l hoa ho~t dQng cua chung bAng l¢nh Ack vit Ready. DOi.~n chlIang trlnh VHDL dlIai day m6 ts. hm.H dQng ella hal qua Irlnh n6i tren. 11-)9 190 entity HandShake is port( eLK : in IllT: DIn : in integer; DOue out inte~cr ); end IlandShakc; Data· in Process A - Ready Data Process out - • B ACK - HLnh 6.12. },if) hlnh tLrOng tac gWa hai qua tdnh proc('ss. architecture Protocol uf HandShake is signal Ready. Ack: nIT; signal Data: integer; begin Send: process begin Ready <;::::' I'; Data <::::: DIn; wait until CLK'cvent and CLK ::::: 'I' and Ack ::::: '1'; Readv <== '0'· . . w'lit until CLK'event and CLK == '1' mul Ack == '0'; end process Send; Receive: prucess begin Ack <~ '0'; wait until CLK'evcnt and CLK == '\' and Re:'ldy == '\ '; DOut <= Data; Ack<=='J'; wait until eLK'event and CLK == 'I' and Ready = '0'; end process Receive; end Protocol; . 111('/1 > ' < {ell fill IIh'JI > J - - . - - . l until < hilill tM(c fo,<ic >] - - < [for < bi/lI_flufc_tllrfi_MiulI >1; Gill l¢nh wait. tren. 1 1-) 9 190 entity HandShake is port( eLK : in IllT: DIn : in integer; DOue out inte~cr ); end IlandShakc; Data· in Process A - Ready Data Process out - • B ACK - HLnh. haa 8 -& gt; 3 duqc 111(1 t,'l bang dm.1l1 ehu'ong trlnh VHDL duai day: entity Encoder is port (yl. y2, y3. y4, yS, y6, y7: in BIT; Vec: out BI1''-VECTOR