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Tandy 1000 Technical Reference Manual

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Tandy 1000
Technical Reference Manual
8272A
Table
9.
Sector
Size Relationships.
FORMAT
SECTOR
SIZE
N
SC
GPl
1
GPL
2
REMARKS
SECTOR
SIZE
N
SC
GPL'
GPl
2
FM
Mode
128
bylesiSeelar
00
lA
07
lB
IBM
Diskette
1
128
byles/Sector
00
12
07
09
256
01
OF
OE
2A
IBM
Diskette
2
128
00
10 10
19
512
02 08
lB
3A
256
01
08
18
30
1024
03
O'
47
8A
512
02
O.
.6
B7
2048
O.
02
C8
FF
1024
03 02
C8
FF
'096
05
01
C8
FF
2048
O'
01
C8
FF
MPM
Mode
256
01
lA
OE
36
IBM
D,skelte
20
256
01
'2
OA
OC
512
02
OF
'B
5'
256
0'
'0
20
J2
1024
03 08
35
7.
IBM
DisketTe
20
512
02
08
2A
50
2048
O'
O'
gg
FF
1024
03
O'
BO
FO
'096
D5
02
C~
FF
2048
O'
02
C8
FF
8192
06
01
C8
FF
4096
05
0'
C8
FF
Nole:
1
SUQgested
values
of
GPl
in
Read
or
Write
Commands
to
avoid
splice
pOint
between
dala
tleld
and
10
field
01
contlQuOus
sections
2
Suggested
values
or
GPL
In
format
command
SCAN
COMMANDS
If the FDC
encounters
a Deleted Data
Address
Mark
on
one
of
the
sectors
(and SK =
0),
then
it
regards
the
sec-
tor
as
the
last
sector
on
the
cylinder,
sets
CM
(Control
The
SCAN
Commands
allow
data
which
is
being
read
from
the
diskette
to
be
compared
against
data
which
is
being
supplied
from
the
main
system
(Processor
in
NON-DMA
mode, and DMA
Controller
in
DMA
mode)
The FDC
compares
the
data
on a
byte-by-byte
basis,
and
looks
for
a
sector
of
data
which
meets
the
conditions
of
D
FDD
=DProcessor, D
FDD
~
DProcessor, or D
FDD
~
DProcessor
Ones
complement
arithmetic
is used
for
comparison
(FF =
largest
number,
00 =
smallest
number).
After
a
whole
sector
of
data
is
compared,
if
the
conditions
are
not
met,
the
sector
number
is
incremented
(R
+
STP'-
R),
and
the
scan
operation
is
continued.
The scan opera·
tion
continues
until
one
of
the
following
conditions
oc-
cur;
the
conditions
for
scan are
met
(equal, low,
or
high),
the
last
sector
on
the
track
is
reached (EaT),
or
the
ter·
minal
count
signal
is received.
If
the
conditions
for
scan are
met
then
the
FDC
sets
the
SH (Scan
Hit)
flag
of
Status
Register
2 to a 1 (high), and
terminates
the
Scan
Command.
If
the
conditions
for
scan are
not
met
between
the
starting
sector
(as
specified
by
R)
and
the
last
sector
on
the
cylinder
(EaT).
then
the
FDC
sets
the
SN (Scan
Not
Satisfied)
flag
of
Status
Register
2
to
a 1 (high). and
terminates
the
Scan
Command.
The
receipt
of
a
TERMINAL
COUNT
signal
from
the
Processor
or DMA
Controller
during
the
scan
operation
will
cause
the FDC
to
complete
the
com·
parison
of
the
particular
byte
which
is in
process,
and
then
to
terminate
the
command.
Table 10
shows
the
status
of
bits
SH and SN
under
various
conditions
of
SCAN
When
either
the
STP
(contiguous
sectors
STP =
01,
or
alternate
sectors
STP
=02
sectors
are read)
or
the MT
(Multi-Track) are
programmed,
it
is
necessary
to
remember
that the
last
sector
on
the
track
must
be
read
For
example,
if
STP
=02, MT =
0,
the
sectors
are
numbered
sequentially
1
through
26, and
we
start
the
Scan
Command
at
sector
21;
the
following
will
happen.
Sectors
21, 23,
and 25
will
be read, then
the
next
sector
(26)
will
be
skipped
and
the
Index
Hole
will
be en·
countered
before
the
EaT
value
of
26
can be
mad
This
will
result
in an
abnormal
termination
of
the
command.
If
the
EaT
had been set at 25
or
the
scanning
started
at
sector
20,
then the
Scan
Command
would
be
completed
in a
normal
manner
The
read/write
head
within
the
FDD
IS
moved
from
cylinder
to
cylinder
under
control
of
the Seek
Command
The FDC
compares
the
PCN (Present
Cylinder
Number)
which
is
the
current
head
position
with
the NCN (New
Cylinder
Number),
and
performs
the
following
operation
if
there is a
difference:
PCN < NCN:
Direction
signal
to
FDD set to a I (high),
and
Step
Pulses
are
issued.
(Step
In)
PCN >
NCN:
Direction
signal
to FDD set
to
a a(low)
and
Step
Pulses
are
issued
(Step OuL)
The rate at
which
Step
Pulses
are
issued
is
controlled
by
SRT
(Stepping
Rate Time) in Ihe SPECIFY
Comrnalld
After
each
Step
Pulse
is
issued
NCN
IS
cornpared
against
PCN, and
when
NCN
= PCN, then the
SE
(Seek
End) flag is
set
in
Status
Register
ato a 1 (high). and the
command
IS
terminated
During
the
Scan
Command
data
is
supplied
bv
either
the
processor
or
DMA
Controller
for
comparison
against
the
data
read
from
the
diskette.
In order
to
avoid
nav'og
the
OR (Over Run) flag
set
In
Status
Register
1,
It
is
nec-
essarv
to
have the
data
available
In
less than 27
~s
IFM
Mode)
or
13
~s
(MFM
Mode) If an Overrun
occurs
tne
FDC
terminates
the
command
SEEK
Mark) flag
of
Status
Register
2
to
a 1 (high) and ter·
minates
the
command.
If SK =
1,
the
FDC
skips
the
sec-
tor
with
the
Deleted
Address
Mark, and reads
the
next
sector.
In
the
second
case (SK =
1),
the
FDC
sets
the CM
(Control
Mark) flag
of
Status
Register
2 to a 1 (high) in
order
to
show
that
a
Deleted
Sector
had been en·
countered.
D
FDO
=
Dprocessor
DFDD*
Dprocesso'
Table
10.
Scan
Status
Codes
Scan
Equal
Scan
Low
Ot
Equal
Scan
HIQhor
Equal
6-233

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Tandy 1000 Specifications

General IconGeneral
ProcessorIntel 8088
Processor Speed4.77 MHz
RAM128 KB (expandable to 640 KB)
Operating SystemMS-DOS 2.11
ManufacturerTandy Corporation
Release Year1984
StorageSingle or double 5.25" floppy disk drive (360 KB), optional hard drive
SoundTandy 3-voice sound
PortsParallel, Serial
GraphicsCGA (Color Graphics Adapter)
Graphics Modes320x200, 640x200

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