Intel MCS48 User Manual page 375

8291
PIN
DESCRIPTION
Symbol
I/O Pin
No. Function
D0-D7
RS0-RS2
I/O
12-19
21-23
CS
RD
WR
INT
(TNT)
DMA
REQ
DMA ACK
TRIG
CLOCK
RESET
I
9
I
10
O
11
O
6
I
&
O
5
DIO1-DIO8
I/O
28-35
DAV
I/O
36
Data bus
port, to
be connected
to
microprocessor
data bus.
Register select inputs, to
be con-
nected
to
three
non-multiplexed
microprocessor address bus
lines.
Select
which
of
the
8 in-
ternal read
(write)
registers
will
be
read
from
(written
into)
with
the execution
of
RD
(WR).
Chip
select.
When
low,
enables
reading from or writing
into the
register selected by RS0-RS2.
Read
strobe.
When
low, selected
register
contents are read by
the
CPU.
Write
strobe.
When
low,
data
is
written into
the selected
register.
Interrupt request
to
the micro-
processor,
set
high
for
request
and
cleared
when
the appropri-
ate register
is
accessed by
the
CPU. May
be software config-
ured
to
be active low.
DMA
request, normally
low, set
high
to indicate
byte output or
byte
input,
in
DMA
mode;
reset
by
DMA
ACK.
DMA
acknowledge.
When
low,
resets
DMA REQ
and
selects
data in/data out register for
DMA
data transfer (actual trans-
fer
done
by
RD/WR
pulse).
Trigger
output,
normally
low;
generates
a triggering pulse cor-
responding
to
the
GET
com-
mand.
External clock
input,
used
for
internal time delays generator.
May
be any speed
in
1-8
MHz
range.
Reset
input.
When
high, forces
the device
into
an
"Idle" (initiali-
zation)
mode. The
device
will
re-
main
at "Idle"
until
released
by
the microprocessor.
8-bit
GPIB
data
port,
used
for
bidirectional data byte transfer
between
8291 and
GPIB
via
non-
inverting external
line
trans-
ceivers.
Data
valid;
GPIB
handshake
control
line.
Indicates the avail-
ability
and
validity of infor-
mation
on
the
DIO
lines.
Symbol
I/O Pin No.
Function
NRFD
I/O
37 Not ready for data;
GPIB hand-
shake
control
line.
Indicates the
condition
of
readiness of de-
vice(s)
connected
to the
bus
to
accept
data.
NDAC
I/O
38 Not data accepted;
GPIB
hand-
shake
control
line.
Indicates the
condition
of
acceptance
of
data
by
the device(s)
connected
to
the bus.
ATN
I
26
Attention;
GPIB command
line.
Specifies
how
data
on
DIO
lines
are
to
be
interpreted.
TFc
I
24
Interface clear;
GPIB
command
line.
Places the interface func-
tions
in
a
known
quiescent
state.
SRQ
O
27 Service request;
GPIB command
line.
Indicates the
need
for
attention
and requests an
inter-
ruption of
the current
sequence
of
events
on
the
GPIB.
REN
I
25
Remote
enable;
GPIB command
line.
Selects
(in
conjunction
with
other
messages) remote
or
local
control
of
the device.
EOi
I/O 39
End
or
identify;
GPIB command
line.
Indicates the
end
of
a
multiple byte transfer
sequence
or, in
conjunction
with
ATN,
addresses the device during
a
polling
sequence.
T/R1
O
1
External transceivers control
line.
Set high
to
indicate output
data/signals
on
the
DIOi-DIOs
and
DAV
lines
and
input signals
on
the
NRFD
and
NDAC
lines
(active
source handshake). Set
low
to
indicate input data/
signals
on
the
DIOi-DIOs and
DAV
lines
and output
signals
on
the
NRFD
and
NDAC
lines (ac-
tive
acceptor handshake).
T/R2
O
2 External transceivers control
line.
Set high to indicate output
signals
on
the EOI
line.
Set low
to indicate
expected
input signal
on
the
EOI
line
during
parallel
poll.
Vcc
PS.
40
Positive
power
supply (5V
±
10%).
GND
P.S.
20
Potential
ground
circuit.
Note:
all
signals
on
the 8291 pins are specified with positive
logic.
However, IEEE 488
specifies negative
logic
on
its
16 signal
lines.
8-85
00229A