Intel MCS48 User Manual page 376

8291
8291
SYSTEM DIAGRAM
MICROPROCESSOR SYSTEM
BUS
IT.
DMA
|
|
CONTROLLER
'
(OPTIONAL)
DRQ
8291
GPIB
INTERFACE
T/R2
J
DACK
T/R1
NON-INVERTING
BUS
TRANSCEIVERS
GENERAL
PURPOSE INTERFACE BUS
THE GENERAL PURPOSE INTERFACE
BUS
(GPIB)
The
General Purpose
Interface
Bus (GPIB)
is
defined
in
the
IEEE Standard
488-1975
"Digital Interface
for
Programmable
Instrumentation."
Although
a
knowledge
of this
standard
is
assumed,
Figure
1
provides the
bus
structure
for
quick
reference. Also,
Tables
1
and
2
reference the
interface state
mnemonics
and
the interface
messages
respectively. Modified
state
diagrams
for the
8291 are presented
in
Appendix
A.
GENERAL
DESCRIPTION
The
8291
is
a microprocessor
controlled device
de-
signed
to interface microprocessors
e.g.,
8048, 8080,
8085,
8086
to the
GPIB.
It
implements
all
of
the interface
functions defined
in
the
IEEE 488
Standard.
If
an
imple-
mentation
of
the Standard's Controller function
is
desired,
it
can be connected
with
an
Intel®
8292
to
form
a
complete
interface.
The
8291 handles communication between
a microproc-
essor controlled device and
the
GPIB.
Its
capabilities
in-
clude data
transfer,
handshake
protocol,
talker/listener
addressing procedures, device
clearing
and
triggering,
service request,
and
both
serial
and
parallel
polling
schemes.
In
most
procedures,
it
does
not disturb the
microprocessor unless
a byte
is
waiting
on
input or
a
byte sent on
output (output buffer empty).
The
8291 architecture includes 16
registers.
Eight of
these
registers
may
be
written into
by the microprocessor.
The
other
eight registers
may
be read by the
microprocessor.
One
each
of
these read and
write registers
is
for direct
data
transfers.
The
rest of
the write registers control the
various
features
of
the
chip,
while the
rest of
the read registers
provide the
microprocessor with a monitor
of
GPI B
states,
various
bus
conditions,
and device conditions.
.
k
111
/\
>.
DEVICE A
ABLE TO
TALK,
LISTEN,
AND
CONTROL
(e.g.
calculator}
C
1
DATA
BUS
DEVICE B
ABLE TO
TALK AND
LISTEN
(e.g. digital
multimeter)
(
'
c
CONTROL
DEVICE
C
ONLY
ABLE
TO
LISTEN
(e.g. signal
generator)
c
N
<
c
C
--
~-
\
MANAGEMENT
1
DEVICE D
ONLY
ABLE
TO TALK
(e.g.
counter)
'
.
'
'
•
'
)-DIO
1
... 8
L*~'*«
ATN
a
nriM
Figure
1.
Interface Capabilities
and Bus
Structure.
8-86
00229
A