Rea d .
A
" low'' on th i s input p i n enab l e s the
8 2 5 5A
to send the data or status
in f o rma t ion to the
CPU
on the data bus .
In es sence , i t al l ows the
CPU
to " rea d
f rom" t he
8 2 55A.
(WR)
W r i t e .
A
" low" on th i s input p i n enab l e s the
CPU
t o w r i t e data or con t ro l
words i n t o t he
8 2 5 5A.
( Ao and
A1 )
Po r t Se l ec t
0
and Port S e lect
1 .
The s e inp u t s igna l s , in con j unc t ion w i th the
RD
and
WR
inpu t s , con t r o l t he se l e c t i on of one of the three ports or the
cont ro l wor d reg i s te r s . The y are norma l ly conne c t e d to the l eas t s ignif icant
b i t s o f t he a ddre ss bus
(Ao
and
A1 ) .
8 2 5 5A BAS IC OPERATION
-
-
-
A
Ai
RD
WR
cs
INPUT OPERAT I ON ( READ )
0
0
0
1
0
PORT A
= = =
�
DATA
BUS
0
1
0
1
0
PORT B
====7
DATA BUS
1
0
0
1
0
PORT
c
= = =
;;:;
DATA
BUS
OUTPUT OPERATION (WRITE )
0
0
1
0
0
DATA BUS
PORT A
0
1
1
0
0
DATA BUS
PORT B
1
0
1
0
0
DATA BUS
= ==
=?
PORT
c
1
1
1
0
0
DATA BUS
===
�
CONTROL
DISABLE FUNCTION
X
X
X
1
DATA BUS
==
=9
3-STATE
1
0
1
0
I LLEGAL CONDITION
X
1
1
0
DATA BUS
= =
=9
3-STATE
( RE SET)
Re s e t .
A
"h igh " on th i s inpu t c l ears the con t ro l reg i s ter and a l l port s
(A, C ,
C )
a re s e t t o t he inpu t mode .
4 . 52
Содержание MKI
Страница 1: ...SERVICE TECHNICAL MANUAL VOL 1 l SVI318 328 MKI MKII COMPUTER SYSTEM SVI SPECTRAVIDEO ...
Страница 7: ...4 Remove the seven retaining screens 5 Remove the cover 2 2 ...
Страница 8: ...6 Remove the screens on the metal cover 7 Remove the metal cover 2 3 ...
Страница 9: ...To r e assemble u se the above procedures in the rever se order 2 4 ...
Страница 134: ...5 CIRCUIT SCHEMATIC AND COMPONENT LAYOUT 5 1 ...
