Sharp CE-150 - Page 315

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3-4-2. Wait control
Q) Function
\\
1
ait is a function appli ed in acc ess in g a s(()\\I <1c 1ion rnen1or y. lt mak es lhc Cl'U
operation ten 1p o rari1 y halted until a cornplctc acc es s is do11c to the s 1(>\ V action
memory. When the CPU make s access to the addr e ss where slow action me mo ry is
assigne d. th e c on dition .. I .. is entered to the wait c ondi t io n in puts WO and W I. WO is
the wait co ndition input whi ch is appl ied to place wait to the me mor y area controlled
by MEO . while WI is the wa it co ndition for the m emo ry ar ea con tr o ll ed by ME I.
Wh en the wait condition is esta blished. that is. wh en " WO · M EO+ WI· M El= I" is met.
the
W /\ IT si gna l is issued to the CP U. As the wait contro l c ou nt er is pro vi de d
internally. it
releases WA IT to the CPU when it is count ed 10 the value set by the
program. then the
CPU proceeds to execute a n ext machine cycle.
AD
M EO
1' 10 __/
WA IT
<'-- - rnc rcn1enls couri ~ c r --- ~ V IAil 1c!cascd
Dt.n· '. O
< -- t P - ~ 11\ ----'>
Since a slo\v access n1cn1ory usu ally co nsis ts of dyn an1i c log ic. it n ee ds a prcchar gc ti n1 c
(t r). Th us . the 1/ 0 po rt controller i ssues the mem ory enab le signals DM EO a nd
!)MEI to the d yn am ic memory . includ ing the prechargc ti rne. DM EO is for M EO
and DME I is for M E I.
When the CPU accesses th e 1/ 0 port co ntr oll er . the sig nal WAI T is i ssued witho ut
the
wait co nditi on in· WO and W I.
0 Wait time
Wait time cim he programmed by me ans of bit positions of GS. 6 and 7 of the G
registe
r. Relati on of GS. 6.7 with IA and tr refer to pag e 70.
75
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