JUKI 6100 Technical Manual page 60

During
the
power on
initialization
cycle port
3
of the
8031/8051
is
programmed
to act
as
an asynchronous
serial
I/O port for
communications with
the
SCU
board.
The sequence
by which
the
MCU-1
board transfers
data to the
SCU-1
board
is
shown
in
the timing
diagram
of
Fig.
7.15.
When
the
SCU
is
prepared to receive
date
it
raises
the
SRDY
line
to the
MCU.
The
SRDY
line
causes
an interrupt to
the processor
and
at
the
end
of the current instruction cycle the processor will
branch to
a
subroutine
to transmit
a
byte of
data to the
SCU
via
the
MTXD
line.
The transmitted data begins
with a start bit
followed
by
eight
data
bits,
a
ninth
bit
which
is
programmable and
a
stop
bit.
The
ninth
bit
can be used to indicate
that
the byte
is
for control or
address purposes.
SRDY (MCU
*-
SCU)
\START/WX3TXWY3TX"pTT^y3FX
"D7
yTB~y
stop
MTXD
(MCU
^
SCU)
Fig.
7.
1
5
MCU
to
SCU
normal
data transfer
When
the
SCU
encounters an
error
condition
it
requests to
send data
to the
MCU
by
raising
a
line
called
SDATA.
The
MCU
responds
to
this
request
by
raising
its
MRDY
line
to indicate that
it
is
prepared
to
accept the error data
from
the
SCU.
The
SCU
will
then transmit
the data byte
and drop
its
request
line.
The
MCU
will
drop
the
MRDY
line
and depending on the
type of
error
which
occurred the pro-
cessor
may
indicate
an
error
condition
on
the
operation panel or retry the
last
operation.
The
diagram
in Fig.
7.16
illustrates
the
sequence
by which
the
SCU
transfers the error
information to the
MCU.
SDATA
(MCU
<-
SCU)
J
MRDY
(MCU
-> SCU)
\sj^/(j5oX~m~Y~v^
stop
-
STXD (MCU
«- SCU)
Fig. 7.
1
6
SCU
to
MCU
error data transfer
Fig.
7.17
is
a
timing diagram of the
parallel
interface lines
and
certain
MCU-1
internal
control
lines
during the transfer
of one
byte of data
from
the
Host
CPU.
The
sequence
to
process the
incoming
data begins
with the
STROBE
line
of the
interface
going
from
a
high to a
low condition.
The
negative transition of the
STROBE
line
causes port
C
bit
1
(port
A
buffer
full)
to
go
high.
The
output of
port
C
bit
1
is
fed
to a
busy
circuit
which
results in
the
signal
MCU-1
BUSY
being
sent to the parallel interface
on
pin 11.
When
the
STROBE
line
goes
back
to
its
high condition the
8155
causes port
C
bit
0 (port
A
interrupt) to interrupt the
MPU. When
the
MPU
finishes
its
current instruction cycle
it
will
branch
to a
subroutine
which
first
places
a
BUSY
condition
on
port
1
bit
1
to the
busy
circuits.
Next
the
MPU
will
read the data
from
port
A
of the
8155 and determine
if
it is
printable data or
a
control code.
The
negative transition
of
the
RD
line
to
the
8155
resets
port
C
bit
0 and during the positive transition
of the
RD
line
the
data
is
latched
in
the
MPU
and
the
8155 port
C
bit
1
is
reset.
-
57
-