DP8496 datasheet(20/92 Pages) NSC

20 / 92 page

40 Functional Description (Continued)

43 DISK DATA CONTROLLER

The Disk Data Controller is concerned only with the data

aspects of the disk drive Control signals for head move-

ment head selection track zero detection etc are left to

the processor or through an external IO port Because of

this the DP84967 can easily be used in a wide variety of

SCSI disk systems

Track format is specified through the internal pattern and

count registers loaded by the host processor at initialization

A unique format can be developed for each application tak-

ing into account speed tolerances PLL lock-on time and

write splice length etc

An additional field before the Header and Data Preambles

(Header Gap and Data Gap) controls RGATE vs WGATE

assertion times This assures that the PLL never sees a

write splice between the header and data field Byte count

programmability of these fields ensures that minimum track

area for the write splice

The data field length (sector size) can range from 16 kBytes

to 64 kBytes with a two byte resolution

Finally both the ID and Data portions of the sector can be

protected with CRC or ECC ranging in length from 16 bits

(CRC) to 32 48 or 56 bits (ECC) All the polynomials are

fixed computer generated codes except the 16-bit CRC

which is a CCITT standard Very little processor overhead is

needed for disk data error correction due to on-chip logic

Additional features include a Sector or Index pulse interrupt

option This makes processor monitoring of disk rotational

speed easier and also location of sectors based on time

since last index pulse for soft sectored drives or count of

sector interrupts for hard sectored drives Also programma-

ble control over AME and AMFSector pins supports pseu-

do-hard sectored (ESDI soft sectored) as well as hard and

soft sectored drives

All registers are buffered such that individual bits will not

change while RD strobe is active except where specified

431 Command Operation

User issues disk commands by writing to the Disk Com-

mand register (DCMD 10h) after format registers and other

disk control registers have been specified Most disk com-

mands follow the flowcharts shown in

Figures 43 44 and

45 The command will begin after the starting condition

specified by the SCT (Start Control) bit in the Disk Com-

mand register and the DCOZ (Drive Command On Zero) bit

in the Timer Prescale register Each command is really bro-

ken into two sub-commands a Header Segment command

and a Data Segment command If a single sector command

is issued (determined by the MSO (Multi-Sector Operation)

bit in the Drive Control register) the command will terminate

at the end of the specified sector Multi-sector commands

will update the Sector Number register and the Sector

Count register after processing each sector and will contin-

ue until the Sector Count register reaches zero

TLF11212 – 10

FIGURE 43 Disk Command Flowchart

DP8496 Datasheet(PDF) 20 Page - National Semiconductor (TI)

DP8496 Datasheet(HTML) 20 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

Datasheet Download

Link URL