Datron 1061 - Ieee Digital Interface; ROM Circuit

3.11
¡EEE
488
STANDARD
D|G|TAL
INTEBFACE
(Circuit
Diasram
No.43O427)
The
IEEE
Digital
lnterface
assembly
conta¡ns
the
extra
memory
circuitry
required
for
the
execution
and
decoding
of
interface
tun"tions,".i¿;;;;;i;
l;o"t
and
output
transfers.
Simplified
diagram
Fis.
3.50 shows
its essential
features.
46
[1lFor
further
information
refer
to
'Getting
aboard
the
488
Bus'published by Motorola.
3.11.1
ROM Circuit
The
IEEE Digital
lnterface assembly acts as an
extension to
the Digital
assembly with connections to
both the
Processor Address
and Datd
Buses. The board
houses
4k bytes of
program
memory
(M3)
containing the
sub-routines
to control the
instrument from
the IEEE
488
Bus.
The ROM
receives
the address information,
with chip
selection
being made
by decoding address
lines
A3-41 1
with XIOBD and
master clock
Ø2.
3.1 1.2
lnterface Circuit
The General
Purpose lnterface Adaptor
(GPIA).
M9,
provides
the
interface between the IEEE
488 Standard
lnstrument
Bus
and the 68000 microprocessor.
The MPU
can
receive,
process
and send
messages
to the interface
through the GPIA.
The
GPIA
is able to
automatically
handle
the follow-
ing
interface
protocal
[1
]
:'
Single
address
capability
Source
and
acceptor
handshake
Talker and Listener
states
Service
Request
Parallel
Poll
Device
Clear
Device
Trigger
W¡th MPU
it is also
capable of:'
Programmable lnterrupts
Storing
the
instrument's
address
Control of
the
ínterface
inputr'output
buffers.
The GPIA
is selected
by decoding
address
lines
A3'
All with XIOBD.
Address
lines A0-42
with
the
state
of
the
MPU R/W
tine
select one of the I
read only
or
7 write-
only registers
in the GPIA,
enabling
the
MPU
to
send
or
receive data over
the
interface.
The
two
signals T/F1
and TlR2
are used
to
control
low
power
transceivers
(formed
from
M1,
2) which
drive
the interface bus.
INPUT. /
OUTPUT
BUFFERS
Ml
M2
GP¡A
M9
DO-D7
INPUT
BU FF ERS
M6
ADDRESS
swrrcHEs
4k
byte
ROM
'AO
D0
Ð7
M3
Fig. 3.50 SIMPLIFIED
DIAGRAM OF
IEEE
ASSEMBLY
TO
IEEE
488
BUS
TO
DIGITAL
ASSEMBLY
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