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READADOBESS
SEQUENCE
RE5ET BUSY
SETINTRQ
SETRNF
TRANSFER TRACK
NUMBERTOSECTOR
REQISTOn
TYPE 111 COMMAND
Read Track/Address
STATUS REGISTER
Upon recelpt of any command, except the Force Interrupt
command, the Busy Status bit Is set and the rest oi the
Status bits are updated or cleared for the new command. If
the Force Interrupt Command is received when there Is a
current command under executlon, the Busy Status bit is
reset, and the rest of the Status blts are unchanged. II the
Force Interrupt command Is recetved when thsre is not a
current command under executlon, ths Busy Status bit is
reset and the rest of the Status bits are updated or cleared.
In this case, Status reflects the Type 1 commands.
The user has the Option of reading the Status register
through program control or uslng the ORQ line with OMA or
Interrupt methods. When the Data register is read 1ha DRQ
bit in the Status register and the DRQ line are automatically
reset. A write to the Data register also causes both DRQ's
to reset.
The busy bit in the Status may be monitored with a user
program to determine when a command is complete, in
lieu of using the INTRQ line. When using the INTRO, a busy
Status check is not recommended because a read of the
Status register to determine the condition of busy will reset
the INTRQ lins.
The format of the Status Register is shown below:
(BITS)
7
S7
6
S6
5
S5
4
S4
3
S3
2
S2
1
S1
0
so
Status varies according to the type of command executed
as shown in Table 4.
Because of intemal sync cycles, certain time dslays must
be observed when operating under programmed WO. They
are: (times double when dock = 1 MHz)
Operation
Write to
Command Reg.
Write to
Command Reg.
Write Any
Register
Next Operation
Read Busy Bit
(Status Bit 0)
Read Status
Bits 1-7
Read From Diff.
Register
Delay Req'd.
FM
'
MFM
12ps
!
6hs
28fiS
i
14fis
0
j
0
I
IBM 3740 FORMAT - 128 BYTES/SECTOR
Shown below is the IBM single-densily format with 128
bytes/sector. In order to format a diskette, ths user must
issue the Write Track command, and load the data register
with the lollowing values. For every byte to be written, there
is one Data Request
57
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