Book of microprocessor and interfacing

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321. 6
Direct Memory
(DMA) - 8237/8257
I~ mOcrvf""" "T _ . )'>Ie.... dot.l tromler c.on br """trolled by <"itt- ..,frw.~ or
""nlw.~. Upt<> rhlo "","01 w~ hoY<' ........ program jns""'liono to tr.n., r.". d.to from 1/0
<!<vi« to m<mOf)' or from """""')' .... 1/ 0 <!<V;,;... To ',.....fu dolo by 11110 """hod
m;,:oop<o« " No. to do following ...ks :
I. To fetch "'" instru<bon
2. To d.t.:ode "'" inotnxtion .nd
" To nccute I"" instructioo.
To CArryOOI ,...... ...." ..,iuop""« .'" ""Iu;"" ronsid.<f..1< Ii....,. 00 this mo<hod 01
dolo lr.mIer .. rot ...itow. for 1o'S'" d.ta rr",.feB IlUCh .. dot. tr.mIer from ....gn<"Ii<
d isk Of op!i<ol d.... 10 -.....y_ In .",h "'tu.ti<>m I""dw.... """trolled do'" ....,..,.,.
~Io_ .
Softw.... Control.... DIU. T,.".t.<
'" this method P"'V'''''''''' ..."""...... ..,.;., 01 .....,ructioN; to arry ""t do.. transkf.
no. ......pl< IIow d.Irt and prosr.", ""lui"'" to tr..,.r..~ do.. from memory to 110 clevie<
is shown In Fig. 1>.1. (Rm-r Fij:. 6.1 or> r>e>.t page.)
""",am ,
T.....'•• S~b_Hn.
HO'J ex. COONT
HO'J ox. POU odd.
""c~ HOY AL , [.11
00't OX. AL
!!<C Ox
INC 51
LOOP BACK
'"H..d• •• Coo"".,d DaU. Trani""
Inlt l olln CQunte.
L<>ad port .<!d,.as in OX
Go. by'. f'''''' ......ory
send byte to output port
lncr._nt port .<!dr.s.
Incr._nt "'''''''Y poin",
R"p.oat uotll e x _ 0
In this lKIIni.q"" ~x"""'l d.-.;a, ill .....:I to ron"'" dot.. tnMn'f. h1em>1 .;..vi«
_ateo odd......nd 000>'''''' ~ t<'qIri<t<l to """troI do .. It&tt!S... . .... allow.
(6 • It

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