Inhaltsverzeichnis
Werbung
Verfügbare Sprachen
Verfügbare Sprachen
record. The FD179X will continue to read or write multiple
records and update the sector register in
numerical
ascending sequence untll the sector register exceeds the
number of sectors on the track or until the Force Interrupt
command is loaded into the Command Register, v/hich
termlnates the command and generates an inierrupi.
For example: If the FD179X is instructed to read sector 27
and there are only 26 on the track, the sector register ex
ceeds the number avallable. The FD179X will search for 5
disk revolutions, Interrupt out, reset busy, and set the
record not found Status bit
The Type II cqmmands for 1791-94 also contain side select
compare flags. When C = 0 (Bit 1) no side comparison is
made. When C = 1, the LSB of the side number is read off
the ID Fleld of the disk and compared with the contents of
Ihe (S) flag (Bit 3). If the S flag compares with the side
number recorded in the ID field, the FD179X continues with
the ID search. If a comparlson Is not made within 5 index
pulses, the injerrupt line is made active and the Record-
Not-Found Status bit is set
The Type II and III commands for the 1795-97 contain a side
select flag (Bjt 1). When U = 0, SSO Is updated to 0.
Similarly, U = 1 Updates SSO to 1. The Chip compares the
SSO to the ID fleld. If they do not compare within 5
revolutions the Interrupt llna is made active and the RNF
Status bit Is set.
The 1795/7 READ SECTOR and WRITE SECTOR com
mands Include a 'L' flag. The L' (lag, in conjunction with
the sector length byte of the ID Fleld, allowsdifferent byte
lengths to be Implemented in each sector. For IBM
compatabillry, the 'L' fiag should be set to a one.
REAO SECTOR
Upon receipt of the Rsad Sector command, the head is
loaded, the Busy Status bit set, and when an ID field is
encountered thal has the correct track number, correct
sector number, correct side number, and correct CRC, tha
data field is presented to the Computer. The Data Address
«W.0 IN SECTOII IEMOTH FIELD
SrOKE KNOTH IN INtEMMl
■tSOTC*
READ SECTOR
SEOUENCB
(mraa
nsn eusi
^\
HTCDCCMM
I
TYPE II COMMAND
TYPE I! COMMAND
52
Werbung
Inhaltsverzeichnis
