IBM Series 1 User Manual page 161
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01
Exte.rnal Sync
The
external
sync capability consists of two signal lines,
an
input line called "external
sync"
and
an
output
line
called
"ready".
A D1
group is set to external sync mode
by
execution
of
the
Arm
DI
External
Sync
command.
When
external sync mode is armed and the system is ready for more
DI data, the ready line from the 01
group
is
set
active.
The user places data on the input points, then activates the
external sync line.
When the
external
sync
line
becomes
active,
the
data
in the DI data register is assumed to be
good and the contents of the register
are
held.
Then
an
interrupt is posted, and the ready line becomes inactive and
stays inactive until the appropriate command, normally
Read
01,
is
executed.
The external sync line must then perform
another transition from the
"0"
to the
"1"
state
to
cause
another interrupt.
External sync mode is reset by an Arm PI command,
a
Device
Reset command, a Halt I/O command, or any reset condition.
Process Interrupt (PI)
A
digital input group is set to
PI
mode
using
the
Arm
PI
command.
The
process
interrupt
function is performed
by
logically ORing the bits
in
the PI data register of
the
DI
group.
That
is,
any
bit
in
the register becoming active
generates an interrupt.
PI
mode
is
reset
by
a
Device Reset Command# a Halt I/O
command, or any reset condition.
The integrated digital I/O feature has two groups of digital
output.
Each
DO
group has:
•
16 output points to the user.
Each
point
provides
a
non-isolated#
unipolar
current
switch
or
TTL
(transistor-transistor
logic)
compatible
output
voltage.
•
One 16-position DO data register.
•
An
"external
sync"
input
line
and a "ready" output
line.
•
Interrupt capability from the external sync input line.
Each
digital
output
group has a unique device address and
responds to specific commands.
Data is stored into
the
DO
data
register
using
the
write
DO
command.
The DO data
register is reset only by a power-on reset.
A
DO group can be tested using three special commands:
(1)
Disable
DO
(2) Read DO,
and
(3)
set
Diagnostic
External
Sync.
The
Disable
DO
command disables the user outputs.
The Read DO command
reads
the
contents
of
the
DO
data
register.
The
set
Diagnostic External Sync command disables
the user outputs and
simulates
the
user's
external
sync
line.
5-4
GA34-0033
c
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