IBM Series 1 User Manual page 162

c
c
0
DO External Sync
The DO external sync capability consists of two signal
lines, an input line called "external sync« and an output
line called "ready".
A DO
group is set to external sync
mode
by
execution of the Arm
DO
External Sync
command. When
a write DO command is executed in external sync mode and the
data on the DO output is good, an active level on the
external sync input line causes the ready line to become
active. The user signifies receipt
of
the data
by
deactivating the external sync line.
Then
an interrupt is
posted, and the ready line becomes inactive.
The
ready line
stays inactive until another Write DO Command is executed
and the external sync input becomes active again. The
external sync line must perform another transition from the
1t1"
to the
"0"
state to cause another interrupt.
External sync mode is reset by a Device Reset command, a
Halt I/O command, or any reset condition.
INTEGRATED DIGITAL I/O OPERATIONAL
CHARACTERISTICS
The timing charts in this section show a logical 'one' as a
down level (typically 0 Vdc), and a logical 'zero' as an up
level (typically
+5
Vdc).
Each DO group can operate in one of three modes:
(1)
non - in t
e
rr up tin
g , ( 2)
ext
e.L n a 1 s
y.n c , an d
(3)
d
ia 9 n
cst i c •
!2.!l=.In!~!:!.J!121ing "od~. When operating
in
the
non-interrupting mode, each DO group of
16
points is
controlled with a write
00
command.
A
logical one written
to a point turns the output transistor on. The output
remains in that condition until the next Write DO command is
executed. The contents of the DO register may be read using
the Read DO command without changing the state of the output
dri Vel's.
Ext~l ~£ Mode. The external sync line permits the user
to control the change of the DO group. The external sync
input meets all of the specifications of a DI point. Figure
5-2 is a timing diagram for DO external sync. This sequence
is executed as follows:
1 •
The external sync mode of operation is initiated by
performing an Arm External Sync command.
2.
The user's external equip.ent signifies that it is
ready to receive new input from the DO group
by
activating the external sync inpu·t (down level) •
3.
The system signifies that the Write DO
command
is
complete and new data is available
by
activating the
ready output (down level).
Integrated Digital I/O 5-5