參數(shù)資料
型號(hào)： TMS279XN
廠商： Texas Instruments, Inc.
英文描述： FLOPPY DISK FORMATTERICONTROLLER FAMILY
中文描述： 軟盤驅(qū)動(dòng)FORMATTERICONTROLLER家庭
文件頁(yè)數(shù)： 17/40頁(yè)
文件大小： 334K
代理商： TMS279XN
TMS279X (WD279X) FLOPPY DISK FORMATTER / CONTROLLER FAMILY
17
step
Upon receipt of this command, the 279X issues one stepping pulse to the disk drive. The stepping motor direction
is the same as in the previous step command. After a delay determined by the r1r0 field, a verification takes place
if the V flag is on. If the T flag is on, the track register is updated. The h bit allows the head to be loaded at the
start of the command. An interrupt is generated at the completion of the command.
step-in
Upon receipt of this command, the 279X issues one stepping pulse in the direction towards track 76. If the T flag
is on, the track register is incremented by one. After a delay determined by the r1r0 field, a verification takes place
if the V flag is on. The h bit allows the head to be loaded at the start of the command. An interrupt is generated at
the completion of the command.
step-out
Upon receipt of this command, the 279X issues one stepping pulse in the direction towards track 0. If the T flag is
on, the track register is decremented by one. After a delay determined by the r1r0 field, a verification takes place
if the V flag is on. The h bit allows the head to be loaded at the start of the command. An interrupt is generated at
the completion of the command.
exceptions
On the 2795/7 devices, the SSO output is not affected during Type I commands, and an internal side compare
does not take place when the (V) verify flag is on.
type II commands
The Type II commands are the Read Sector and Write Sector commands. Prior to loading the Type H command
into the command register, the computer must load the sector register with the desired sector number. Upon
receipt of the Type II command, the busy status bit is set. If the E flag = 1 (this is the normal case) HLD is made
active and HLT is sampled after a 15 ms delay. If the E flag is O, the head is loaded and HLT sampled with no 15
ms delay.
When an lD field is located on the disk, the 279X compares the track number on the ID field with the track
register. If there is not a match, the next encountered ID field is read and a comparison is again made. If there
was a match, the sector number of the ID field is compared with 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 then located and will be either written into, or read from depending upon the command. The 279X
must find an ID field with a track number, sector number, side number, and CRC within 5revolutions of the disk;
otherwise, the record not found status bit is set (status bit 4) and the command is terminated with an interrupt.
Each of the Type II commands contains an (m) flag which determines if multiple records (sectors) are to be read
or written, depending upon the command. If m = 0, a single sector is read or written and an interrupt is generated
at the completion of the command. If m = 1, multiple records are read or written with the sector register internally
updated so that an address verification can occur on the next record. The 279X will continue to read or write
multiple records and update the sector register in numerical ascending sequence until the sector register exceeds
the number of sectors on the track or until the Force Interrupt command is loaded into the command register,
which terminates the command and generates an interrupt.
For example: if the 279X is instructed to read sector 27 and there are only 26 on the track, the sector register
exceeds the number available. The 279X will search for 5 disk revolutions, interrupt out, reset busy, and set the
record not found status bit.
The Type II commands for 2791-93 also contain side select compare flags. When C = 0 (bit 11 no side
comparison is made. When C = 1, the LSB of the side number is read off the ID field of the disk and compared
with the contents of the (S) flag (bit 3). If the S flag compares with the side number recorded in the ID field, the
279X continues with the ID search. If a comparison is not made within 5 index pulses, the interrupt line is made
active and the record-not found status bit is set.
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