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2.
Principle of operation
2.1
Program processing
The c o n t r o l f u n c t i o n s o f the lOlU are
d e f i n e d by a user program.
I n order t o be able t o scan the user
program c y c l i c a l l y statement by s t a t e -
ment, t h e CPU has t o perform the f o l l o w -
i n g f u n c t i o n s :
1. I n t h e case o f a c o l d r e s t a r t (power
s w i t c h from " O f f " t o "On" o r mode
s e l e c t o r from "Stop" t o "Run"), t h e
process o u t p u t image* i s erased,
i.e.
a l l o u t p u t s are s e t t o zero.
2. The process i n p u t image* i s updated,
i.e.
a l l s i g n a l statuses o f the i n -
p u t s are scanned and w r i t t e n i n t o
t h e process i n p u t image.
The user program (PB1 o r FBI) i s
scanned and processed statement by
statement. When scanning the s i g n a l
statuses o f t h e inputs, the CPU ac-
cesses t h e process i n p u t image and
n o t t h e a c t u a l inputs. When l a t c h i n g
and u n l a t c h i n g t h e outputs ( c o i l s ) ,
o n l y t h e process output image i s
o v e r w r i t t e n t o begin with.
4. Once t h e user program has been p r o -
cessed, t h e process output image
i s t r a n s f e r r e d t o t h e actual out-
puts.
5. P o i n t s 2, 3 and 4 are handled c y c l i -
c a l ly.
Cold restart
Cr>
Erase process
output image
I
Cycle checkpoint
Read process
input image
12nd statement
I
Last statement
H
Transfer process
I
output image to
the outputs
Fig. 3:
P r i n c i p l e o f operation o f t h e
S5-101U
A scanning o p e r a t i o n from c y c l e check-
p o i n t t o c y c l e checkpoint takes approx.
70 ms f o r 1024 statements ( b i n a r y ) .
I f a scanning c y c l e i s not completed
w i t h i n 300 ms due t o program e r r o r s
*
Process 1/0 image:
o r f a u l t s ,
an i n t e r n a l monitor responds,
I n t e r n a l memory area i n which t h e
t h e P C e n t e r s t h e "Stop" s t a t u s and
s i g n a l s t a t u s ( " 0 " or "1") o f t h e
a l l o u t p u t s ( c o i l s ) are switched o f f .
i n p u t s / o u t p u t s i s stored.
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