DP8496 datasheet(34/92 Pages) NSC

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40 Functional Description (Continued)

Extending the Current Disk Command

Disk commands with the MSO (Multi-Sector Operation) bit

set to ‘‘1’’ in the Disk Command register may be extended

to transfer more sectors than originally programmed If a

new value is written to the Sector Count register while a disk

command is executing the new value will be downloaded

from the holding register to the active register when the

active Sector Count reaches zero A new Disk Pointer will

also be downloaded at the same time if a new value has

been written to the Disk Pointer registers

A new pipelined Sector Count may be written to the Sector

Count register any time before the active Sector Count

reaches zero The Sector Count register should not be up-

dated again (after the first pipelined value) until the previous

pipelined value has been downloaded The ‘‘Group Com-

plete’’ interrupt indicates when a pipelined Sector Count

and Disk Pointer is downloaded After this interrupt is re-

ceived the Sector Count register and Disk Pointer registers

may be updated again

A disk command may be extended multiple times if desired

Simply wait for the ‘‘Group Complete’’ interrupt between

each update of the Sector Count register

Table 416 summarizes these interrupts

Pipelining Disk Commands

Disk commands may be pipelined If a new disk command is

written to the Disk Command register while an operation is

executing the new disk command will be buffered and

downloaded internally when the current command has com-

pleted

To assist in determining when a new disk command may be

written to the Disk Command register for pipelining an inter-

rupt may be used If the HNC (Header CompleteNext

Command) bit in the Disk Interrupt Enable register is set to

‘‘0’’ the ‘‘Next Command’’ interrupt is enabled When this

interrupt occurs a new disk command may be written to the

Disk command register This new disk command will be

downloaded and executed after the current disk command

has completed all of its operations If the current disk com-

mand is multi-sectored the new disk command will not be

downloaded until all the sector operations have completed

The Sector Count register will also be downloaded at the

same time a disk command is downloaded If a new value is

not written to this register the value from the previous

download will be used A new Disk Pointer will also be

downloaded at the same time as the new disk command

but only if the Disk Pointer has been written to since the last

disk command download

Disk commands may be pipelined multiple times if desired

Simply wait for the ‘‘Next Command’’ interrupt between

each update of the Disk Command register

Special Formats

Some applications require tracks that are formatted with

sectors of varying lengths or sectors with different synch

bytes or other unique format variations This requires modi-

fying the header format registers ‘‘on the fly’’ during a for-

mat operation It is important to modify these registers only

while they are not being used by the Disk Data Controller

The processor can use the Interlock mode and the Header

Complete interrupt to allow modification of the disk format

registers for the ID Segment (addresses 21h 23h – 2Fh) or

the Sector Byte Count registers (35h 36h) during the format

operation The Header Complete interrupt is generated after

the Sector Byte Count registers have been downloaded at

the beginning of the data field The processor has until the

Data Postamble field to make any necessary changes to the

desired registers and then write to the Interlock (Header

Byte Count) register telling the DP84967 that changes are

complete If Interlock is not received in time a Late Interlock

interrupt is generated

TABLE 416 Disk Buffer Management Interrupts

Sector

New Disk

New

Command

Count

Command

Sector

Interrupt

Type

Reached

Been

Count

Type

Comments

Zero

Loaded

Been

Loaded

SCI

Interim sector completed of a multi-sector operation

Multi-Sector

Yes

GCI

The last sector of the previous Sector Count has been

transferred tofrom the disk Command is extended with new

Sector Count

(MSO e 1)

Yes

CCI

Previous disk command has completed New pipelined

command is starting

Yes

CCI

Previous disk command has completed No new command

Single

Yes

CCI

Single sector command has completed New pipelined command

is starting

Sector

(MSO e 0)

CCI

Single sector command has completed

Note

MSO (Multi-Sector Operation) bit is in the Disk Command register SCI e Sector Complete Interrupt GCI e Group Complete Interrupt CCI e Command

Complete Interrupt

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