Sharp PC-1500 Technical Reference Manual page 80

A ll
and more about Sharp PC-1 500 at http://www.PC-1500.info
3-4-2. Wait control
Q) Function
\\
1
ait is a function applied in accessing a s(()\\I <1c1ion
rnen1ory.
lt makes
lhc
Cl' U
operation ten1porari1y
halted until
a
cornplctc
access is do11c to
the s1(>\V
action
memory. When the CPU makes access to the address where slow action memory is
assigned. the cond ition .. I .. is entered to the wait condition in puts WO and W I. WO is
the wait condition input which is applied to place wait to the memory area controlled
by MEO. while WI is the wait condition for the memory area contro lled by ME I.
When the wait condition is established. that is. when
"WO· MEO+WI·
M E l= I" is met.
the W /\ IT signal is issued to the CPU. As the wait control counter is provided
internally. it releases WA IT to the C P U when it is counted
10
the value set by the
program. then the C PU proceeds to execute a next machine cycle.
A D
MEO
1' 1 0 _ _ /
WAIT
<'--- rncrcn1enls
couri~cr ---~
VIAil
1c!cascd
Dt.n·' . O
< -- t P - ~
11 \ - - - - ' >
Since a slo\v access
n1cn1ory
usually consists of dynan1ic logic.
it
needs a prcchargc
tin1c
(t r ). Thus. the 1/ 0 po rt controller issues the memory enab le s ignals DM EO a nd
!)MEI to the d ynamic memory. including the prechargc ti rne. D M EO is for M EO
and DME I is fo r M E I.
When the CPU accesses the 1/ 0 port contro ller. the signal
WAI T
is issued without
the wait condition in· WO and W I.
0
Wait time
Wait time cim he programmed by means of bit positio ns of GS. 6 and 7 of the G
register. Relation of GS. 6.7 with
I A
and tr refer to page 70.
75
Do not sale this PDF!!!