PC87306 datasheet(37/110 Pages) NSC

37 / 110 page

40 FDC Command Set Description (Continued)

Notes

TLC12379 – 29

A1 e Data Pattern of A1 Clock Pattern of 0A

C2 e Data Pattern of C2 Clock Pattern of 14

All byte counts in decimal

All byte values in hex

CRC uses standard polynomial x16 a x12 a x5 a 1

Perpendicular Format GAP2 e 41 bytes for 1 Mbps and 2 Mbps

All other data rates use GAP2 e 22 bytes

FIGURE 4-2 IBM Perpendicular and ISO Formats Supported by the Format Command

414 Invalid Command

If an invalid command (illegal Opcode byte in the Command

Phase) is received by the controller the controller responds

with ST0 in the Result Phase The controller does not gen-

erate an interrupt during this condition Bits 6 and 7 in the

MSR are both set to a 1 indicating to the mP that the con-

troller is in the Result Phase and the contents of ST0 must

be read The system reads an 80h value from ST0 indicating

an invalid command was received

Command Phase

Invalid Op Codes

Execution Phase

None

Result Phase

Status Register 0 (80h)

415 Lock Command

The Lock command allows the user full control of the FIFO

parameters after a software reset If the LOCK bit is set to 1

then the FIFO THRESH and PRETRK bits in the Configure

command are not affected by a software reset In addition

the FWR FRD and BST bits in the Mode command are

unaffected by a software reset If the LOCK is 0 (default

after a hardware reset) then the above bits are set to their

default values after a software reset This command is use-

ful if the system designer wishes to keep the FIFO enabled

and retain the other FIFO parameter values (such as

THRESH) after a software reset

After the command byte is written the result byte must be

read before continuing to the next command The execution

of the Lock command is not performed until the result byte

is read by the mP If the part is reset after the command byte

is written but before the result byte is read then the Lock

command execution is not performed This is done to pre-

vent accidental execution of the Lock command

Command Phase

LOCK0010100

Execution Phase

Internal Lock register is written

Result Phase

000LOCK0000

416 Mode Command

This command is used to select the special features of the

controller The bits for the Command Phase bytes are

shown in Section 41 Command Set Summary and their

function is described below These bits are set to their de-

fault values after a hardware reset The default value of

each bit is denoted by a ‘‘bullet’’ to the left of each item The

value of each parameter after a software reset is explained

PC87306 Datasheet(PDF) 37 Page - National Semiconductor (TI)

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