Tandy 1400LT Service Manual page 294

C o m m a n d Symbpl Description
Name Function
Au
(Address Line 0)
A, controls selection of main status
register (A,=O) ro data register
(A,= 1)
C
(Cylinder Number)
C stands for the current/selected
cylinder (track) numbers 0 through
76 of the medium.
D stands for the data pattern which
is going to be written into a sector.
D
(Data)
D, - D u
(Data Bus)
8-bit data bus, where D, stands for a
most significant bit, and
Do
stands for
a least signification bit.
DTL
(Data Length)
When N is defined as 00, DTL stands
for the data length which users are
going to read out or write into the
sector.
EOT
(End of Track)
EOT stands for the final sector
number on a cylinder. During read or
write operations, F D C will stop data
transfer after a sector number equal
to EOT.
GPL stands for the length of gap 3.
During Read/Write commands this
value determines the number of bytes
that VCO sync will stay low after two
CRC bytes. During Format command
it determines the size of gap 3.
G P L
(Gap Length)
H
(Head Address)
H D
(Head)
H stands for head number 0 or 1, as
specified in I D field.
H D stands for a selected head
number 0 or 1 and controls the
polarity of pin 27. ( H = H D in all
command words.)
HLT
(Head Load Timc
HLT stands for the head load time in
.he FDD (2 to 254 ms in 2 ms
increments).
HUT stands for the head unload time
after a Read or Write operation has
occurred (16 to 240 ms in 16 ms
increments).
If M F is low, F M mode is selected,
and if it is high, MFM mode is
selected.
If MT is high, a multitrack operation
is performed. If M T = 1 after finishing
read/write operation on side 0, FDC
will automatically start searching for
sector 1 on side 1.
HUT (Head
Unload Time)
M F (FM or MFM
Mode)
M T
(Multitrack)
Name Function
N
(Number) written in a sector.
N C N (New NCN stands for a new cylinder
Cylinder Number) number which is going to be reached
as a result of the seek operation;
desired Dosition of head.
N stands for the number of data bytes
N D (Non-DMA
Mode) DMA mode.
P C N (Present
Cylinder Number)
N D stands for operation in the non-
PCN stands for the cylinder number at
the completion of Sense Interrupt
Status command, position of head at
present time.
R stands for the sector number which
will be read or written.
R / W stands for either Read (R) or
R
(Record)
R/W
(Read/Write) Write (W) signal.
sc
(Sector) cylinder.
SK
(Skip) address mark.
SC indicates the number of sectors per
SK stands for skip deleted data
SRT
(Step Rate Time)
SRT stands for the stepping rate for
the FDD (1 to 16 ms in 1 ms
increments). Stepping rate applies to
all drives ( F H = lms, EH=2ms, etc.)
STO
-
ST3
(Status 0 - 3)
STO - ST3 stands for one of four
registers which store the status
information after a command has been
executed. This information is available
during the result phase after command
execution. These registers should not
be confused with the main status
register (selected by A,=O). STO -
ST3 may be read only after a
command has been executed and
contains information relevant to that
particular command.
During a scan operation, if STP= 1,
the data in contiguous sectors is
compared byte by byte with data sent
from the processor (or DMA); and if
STP
= 2, then alternate sectors are read
and compared.
STP
us,,
us,
US stands for a selected drive number
(Unit Select) O o r 1.
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