Intel MCS48 User Manual page 380

8291
8291 Registers
A
bit-by-bit
map
of the 16
registers
on
the 8291
is
presented
in
Table
3.
A
more
detailed explanation
of
each
of
these
registers
and
their functions
follows.
The
access
of
these
registers
by
the
microprocessor
is
accomplished
by using the CS, RD,
WR,
and RS0-RS2
pins.
Register
All
Read
Registers
All
Write Registers
Don't Care
CS RD
WR
RS0-RS2
1
ccc
1
ccc
1
X
X
XXX
TABLE
3.
8291
REGISTERS
READ REGISTERS
DI7
DI6 DI5 DI4
OI3 DI2 Oil OIO
DATA
IN
CPT
APT GET END DEC ERR
BO
Bl
INTERRUPT STATUS
1
INT SPAS
LLO
REM
SPASC
LLOC REMC ADSC
INTERRUPT STATUS
2
S8
SRQS
S6
S5
S4
S3 S2 SI
SERIAL POLL STATUS
ton Ion EOI
LPAS TPAS
LA TA MJMN
ADDRESS STATUS
CPT7 CPT6 CPT5 CPT4 CPT3 CPT2 CPT1 CPTO
COMMAND
PASS
THROUGH
X DTO DLO
AD5-0
AD4-0 AD3-0 AD2-0 AD1-0
ADDRESS
X DT1 DL1 AD5-1 AD4-1 AD3-1 AD2-1
ADM
REGISTER SELECT
CODE
RS2
RS1
RSO
1
WRITE REGISTERS
1
1 1 1
D07 DQ6 D05 D04 D03 D02 DOI
DOO
DATA OUT
CPT APT GET END DEC ERR BO
Bl
INTERRUPT
MASK
1
DMAO
DMAI
SPASC
LLOC
REMC ADSC
INTERRUPT
MASK
2
S8
rsv
S6 S5 S4 S3 S2 SI
SERIAL POLL
MODE
TO LO
ADM1 ADMO
ADDRESS MODE
CNT2 CNT1
CNTO COM4 COM3 COM2 COM1 COM0
AUX MODE
ARS DT DL AD5
AD4 AD3 AD2 AD1
ADDRESS
0/1
EC7 EC6 EC5 EC4 EC3 EC2 EC1
ECO
ADDRESS
1
EOS
Data Registers
DI7 DI6 DI5
DI4 DI3 DI2
DM
DIO
DATA-IN REGISTER
(OR)
D07 DO6 D05
D04 D03 D02
DOI
DOO
DATA-OUT REGISTER
(0W)
The
data-in
register
is
used
to
move
data
from the
GPIB
to
the
microprocessor or to
memory when
the 8291
; s
addressed
to
listen.
Incoming
information
is
separately
latched by
this register,
and
its
contents
are not
destroyed
by
a write to
the data-out
register.
The
RFD
(Ready
for
Data)
message
is
held false
until
the byte
is
removed from
the data
in register,
either
by
the
microprocessor or
by
DMA. The
8291 then completes the
handshake automati-
cally. In
RFD/DAV
holdoff
mode
(see Auxiliary Register
A),
the
handshake
is
not finished
until
a
command
is
sent
telling
the 8291 to
release the
holdoff. In this
way, the
same
byte
may
be read
several times, or
an over anxious
talker
may
be
held
off until
all
available
data has
been processed.
8-90
00229A