Graf Elektronik FLO3 Handbuch Seite 53

VERIFY
3E0.UENCE
then located and will be Bither written inlo, or read from
depending upon the command. The FD179X musl find an
ID field with a Track number, Sector number, stde number,
and CRC within lour revolutions o! Ihe dlsk; oiherwlse, ihe
Record not found Status blt Is sei {Status tiit 3) and the
command isterminated with an interrupl.
TYPE I COMMAND FLOW
TYPE IICOMMANDS
The Typs II Commands are the Read Sector and Write
Sector commands. Prior to loading the Type II Command
into the Command Register, Ihe Computer must load the
Sector Register with the deslred sector number. Upon
receipt ot the Type il command, the busy Status Bit is set. If
the E flag = 1 (this is the normal case) HLD is made active
and HLTIs sampled aftera 15 msec delay. If the E flag is 0,
the head la loaded and HLT sampled with no 15 msec
delay. Tha ID fleld and Data Fletd format are shown on page
13.
When an ID fleld is located on Ihe dlsk, the FD179X
compares the TracK Number on the ID fiefd with the Track
Reßlater. If there is not a match, the next encountered ID
fleld Is read and a comparison is again made. If there was a
match, the Sector Number of the ID field is compared wilh
the Sector Register. If there is not a Sector match, the next
encountered ID field is read off the disk and comparisons
again made. If the ID field CRC is correct, the data field is
TYPE II COMMAND
Each o( the Type II Commands conlalns an (m) flag whlch
determlnes if multiple records (sectors) are to be read or
written, dependlng upon Ihe command. If m = 0, a Single
sector is reaü or written and an inlenupt Is generated at the
completion of Ihe command. If m = 1, multiple records are
read or wrilten with the sector reglster internally updated
so tiiat an address variflcation can occur on the next
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