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Table 3. Status Register Identification (coni)
No.
Nanw
Function
Pin
Command Symbol Description
Status
Register
3
D7
FT
(Fault)
WP
(Write Protected)
This bit is used to indicate the status 01 the
fault signal from the FDD.
This bit is used to indicate the status 01 the
write orotected sianal from the FDD.
D5
RY
Dq
TO
D3
TS
Dp
HD
Di
US1
Do
us0
This bit is used to indicate the status of the
ready signal from the FDD.
This bit is used to indicate the status 01 the
track 0 signal from the FDD
This bit is used to indicate the Status of
the
two-side signal from the FDD.
This bit is used to indicate the status of the
side Select signal tothe FDD.
This bit is used to indicate the status 01 the
unit select 1 signal to the FDD.
This bit is used to indicate the status of the
unit select 0 sianal to the FDD.
(Ready)
(Track 0)
(Two-Side)
(Head Address)
(Unit Select 1)
(Unit Select 01
Note:
(1)
CRC= Cyclic Redundancy Check
(2) IOR=
Internal Data Register
(3) Cylinder
(C)
is described more fully in the Command Symbol
Description.
Command Sequence
The pPD765AlpPD7265 is capable of performing 15 dif-
ferent commands. Each command is initiated by a
multibyte transfer from the processor, and the result af-
ter execution of the command may also be a multibyte
transfer back to the processor. Because of this multi-
byte interchange of information between the pPD765AI
pPD7265 and the processor, it is convenient to consider
each command as consisting of three phases:
Command
The FDC receives all information re-
Phase:
quired to perform
a
particular opera-
tion from the processor.
Execution
The FDC performs the operation it
Phase:
was instructed to do.
Result Phase: After completion of the operation,
status and other housekeeping infor-
mation are made available to the
processor.
Table 4 shows the required preset parameters and
results for each command. Most commands require 9
command bytes and return 7 bytes during the result
phase. The " W ' to the left of each byte indicates a com-
mand phase byte to be written, and an "R" indicates a
result byte. The definitions of other abbriviations used
in table are given in the Command Symbol Description
table.
A0
(Address Line
0)
C
(Cylinder Number)
D
IData)
written into a sector.
A0 controls selection of main status register
(Ag=O) or data register (Ao=I).
(track) numbers 0 through 76 otthe medium.
C stands for the current/selected cylinder
D stands for the data pattern which is going to be
&bit data bus, where D7 stands for a most
significant bit. and
DO
stands for a least
significant bit.
When N is defined as
00,
DTL stands for the data
length which users are going to read out or write
into the sector.
EDT stands for the final sector number on a cylin-
der. During read or write operations, FDC will stop
data transfer after a sector number equal to EOT.
GPL stands tor the length
of
gap
3.
During Read /
Write commands this value determines the num-
ber 01 bytes that VCO sync will stay low after two
CRC bytes. During Format wmmand it deter-
mines the size of gap
3.
D7-DO
(Data
Bus)
DTL
(Data Length)
EDT
(End of Track)
GPL
(Gap Length)
H
lHead Address)
ID tieid.
H stands tor head number 0 or 1, as specified in
HD
(Head)
HD stands for a selected head number 0 or
1
and
controlsthepolarityofpin 27. (H=HDinalicom-
mand words.)
H LT
HLTstandsforthe headloadtimeintheFDD(2to
(Head Load Time)
254 ms in 2 ms increments).
HUT
HUT stands for the head unload time after a Read
(Head Unload Time)
or Write operation has occurred (16 to 240ms in
16ms increments).
If MF is low, FM mode is selected. and if it is high,
MFM mode is selected.
IF MT is high, a multitrack operation is per-
formed. if MT = 1 after finishing read / write oper-
ation on side
0.
FDC will automatically start
searchina for sector t on side 1
MF
(FM or MFM Mode)
MT
(Multitrack)
N
(Number)
sector.
NCN
(New Cylinder Number)
ND
1Non-DMA Mode)
N stands for the number of data bytes written in a
NCN stands for a new cylinder number which is
going to be reached as a result 01 the seek opera-
tion; desired position of head.
ND stands tor operation in the non-DMA mode.
PCN
PCN stands tor the cylinder number at the com-
(Present Cylinder Number) pletion of Sense Interrupt Status command, posi-
tion 01 head at present time.
R
R stands for the sector number which will be read
(Record)
or written.
R I W
R I W stands for either Read (R) or Write (W)
(Read
/
Write)
signal.
sc
SC indicafes the number
of
sectors per cylinder.
(Sector)
SK
(Skin)
SK stands lor skip deleted data address mark.
6-12
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