Table of Contents
Advertisement
SECTION
n
PROGRAMMED
l/O
TRANSFERS
This section
is
divided
into the
following parts.
a.
Input/Output Instructions
b.
Input/Output Circuits
c.
Programmed
l/O Bus
Signals
d.
Signal
Timing
e.
List
of
Signals,
Mnemonics,
and Pin Nunnbers
f
.
Interfacing
the
Programmed
l/O Bus
g.
Interrupts with
Recommended
Gating
h.
Example
of a
Programmed
l/O
Interface
I/O
INSTRUCTIONS
The
following
list
of
instructions are
used
to
communicate between
the
program
and
the
external
system.
Part
of
the
hardware
to
execute these
instructions
is
in the
mainframe.
This
hardware
causes
the
various
signals
to
be
propagated on
the
l/O
bus.
The remaining
hardware
to
execute
the
instructions
is
in the
interface
unit.
This
hardware
receives and
transmits
data
and answers
interrogations with
the
proper
pulses.
See
Appendix
B
for
device address
and
mask
bit
assignments.
OCP
-
Output Control Pulse
This instruction
is
used by
the
program
to
command
an
action;
e. g.
,
start the
reader,
reset
the clock,
etc.
The
6-bit
address
field
of this
instruction specifies the action
and
device.
OTA
-
Output Transfer
From
Accumulator,
If
Ready
This instruction
first
deternnines
whether
the
interface
is
ready
for
an
output data
transfer.
If
the interface
is
ready,
a 12-bit
parallel transfer
from
the
accunaulator
to
the
interface takes place
and
the
next sequential instruction
is
skipped.
If
the interface
is
not
ready,
the
transfer does not take place
and
the
next sequential instruction
is
executed.
The
6-bit
address
field of the
instruction specifies
the
recipient of the data.
INA
-
Input
Transfer
to
Accumulator,
If
Ready
As
in the
OTA,
this
instruction
first
determines whether
the
interface specified
by
the
instruction's
address
field
is
ready
to
transfer data
to
the
mainframe.
If
ready,
the
accumu-
lator
is
cleared and
12 bits (or
less) of
data
is
transferred
to
the
accumulator
in
parallel.
If
the interface
is
not ready, the
accumulator
is
cleared, but the transfer
does
not take
place.
2-1
Advertisement
Table of Contents
