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Philips PM2519 - Page 40

Philips PM2519
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2-24
2.8.
2.8.1.
PM
2519/51
1EC-625/IEEE-488
interface
An
IEC-bus
interface
is
used
in
multi-device
systems
to
connect
instruments
in
parallel
to
the
same
interface
lines.
Each
instrument
has
its
own
specific
address
(selected
with
switches
SO-S4
on
the
rear
of
the
instrument}.
This
addressing
system
means
that
an
instrument
is
only
listening
or
talking
after
it
has
received
its
specific
address
(MLA;
my
listen
address,
MTA;
my
talk
address}.
The
listen
or
talk
addresses
are
generated
by
the
controller
of
the
system
(computer)
and
are
transmitted
via
the
data
of
the
bus.
During
an
address
or
interface
message
the
ATN
(attention)
line
is
active
to
indicate
that
the
information
on
the
bus
has
a
special
interface
function.
The
1EC-bus
can
be
split
up
into
three
functional
parts,
the
data
bus,
the
handshake
bus
and
the
management
bus.
—
The
data
bus
is
used
to
transport
messages
for
the
device
functions
as
well
for
the
interface
functions
and
consist
of
8
lines
(DIO1-8).
—
The
handshake
bus
controls
the
correct
transfer
of
data
bytes
with
the
next
three
signals,
Data
valid
(DAV)
indicates
if
the
data
is
valid.
Not
Ready
For
Data
(NRFD)
indicates
the
condition
of
readiness
of
device(s)
to
accept
data.
—
Not
Data
Accepted
(NDAC)
indicates
the
condition
of
acceptance
of
data
bytes
by
devices.
—
The
management
bus
is
used
to
manage
an
orderly
flow
of
information
across
the
interface.
For
this
purpose
the
next
five
signals
are
available:
Attention
Specifies
how
data
on
the
D10
lines
are
to
be
interpreted.
Active
indicates
a
interface
message
is
transferred
via
the
data
bus
(for
example
a
listen
address),
not
active
status
is
present
during
normal
data
transfer
{for
example
a
command
for
ranging).
Interface
clear
IFC
places
the
interface
of
all
interconnected
devices
in
the
idle
state.
Service
request
SRQ
indicates
that
one
of
the
instruments
wants
the
attention
of
the
controller
for
example
to
indicate
that
there
is
valid
data.
Remote
enable
REN
sets
an
instrument
to
its
remote-control
mode
if it is
in
the
addressed
state.
End
of
Identify
OI
indicates
the
end
of
a
multiple
byte
transfer.
When
the
PM
2519/51
is
switched
on,
the
microcomputer
reads
the
switches
to
identify
the
mode
of
the
interface,
Listen-only,
Talk-only
or
Addressable
mode.
After
this
it
sets
the
interface
in
a
condition
to
input
data.
Receiving
First
the
system
controller
sends
a
listen
address
(MLA)
via
the
DIO
lines
(ATN
is
true).
Due
to
ATN
is
true
D604
and
D603
are
switched
to
receive
direction.
Also
via
the
hardware,
NDAC
is
generated.
The
TA
(talker
active)
signal
is
high
so
that
the
input
of
D602
{a
special
GPIB
device)
is
low.
This
means
that
a
part
of
D602
acts
as
input
and
another
part
as
output.
Outputs:
NDAC,
NRFD,
SRQ
D602
Inputs
:
DAV,
REN,
ATN,
EOI,
IFC
Also
after
ATN,
the
microcomputer
reads
the
selected
device
address
by
making
pin
10
of
D605
low
and
input
19
of
D604
high
(high
impedance).
Then
the
microcomputer
starts
handshaking
the
device
address
on
the
bus.
This
is
controlled
via
P1
of
the
microcomputer.
If
the
device
address
on
the
bus
is
the
same
as
the
device
address
selected
with
the
switches,
the
microcomputer
starts
to
handshake
in
the
other
data
bytes.

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