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Teac MT-20D-IO - Page 33

Teac MT-20D-IO
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"D/CAS"
3-4
Interface
control
(PCBA
Interface
Control)
The
PCBA
interface
control
(hereinafter,
referred
to
as
MTC)
controls
the
transfer
of
command/status
and
read/write
data
with
the
host
system
(here-
inafter,
referred
to
as
HOST),
or
performs
data
processing
or
tape
position
control
with
respect
to
the
PCBA
drive
control
(hereinafter,
referred
to
as
GMT)
.
The
main
functions
of
MTC
are
controlled
by
CPU
(U9/80C85A
micro-
processor),
while
the
data
system
requiring
high
speed
transfer
is
controlled
by
DMAC
(U7/82C37
DMA
controller).
The
data
transfer
between
the
individual
blocks
within
MTC
as
shown
in
Fig.
301(a)
is
performed
by
DMAC
in
competition
with
CPU
on
the
CPU
bus
(cycle
stealing
mode).
At
this
time,
however,
this
system
is
programmed
so
that
the
CPU
bus
is
released
to
CPU
once
on
every
DMA
cycle
to
prevent
the
CPU
bus
from
being
occupied
for
a
long
time,
when
data
transfer
requests
are
concentrated,
thereby
assuring
the
worst
operating
ratio
of
CPU.
Description
is
given
below
on
the
operation
of
each
block
of
MTC
(PCBA
interface
control)
shown
in
Fig.
301(a).
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321
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