UPD765B datasheet(10/17 Pages) NEC

10 / 17 page

uPD765A/uPD765B

NEC

Table 3. Status Register Identification

NO.

Name

Status Register 0

D7,

(Interrupt Code)

Function

D7=0 and D6=0

Normal termination of command, (NT)

Command was completed and properly ex-

ecuted

D7=0 and D6=1

Abnormal termination of command, (AT)

Execution

of command was started but

was not successfully

completed.

D7=1 and D6=0

Invalid command issue, (IC) Command

which was issued was never started

D65

D7=1 and D6=1

Abnormal termination

because during

command execution the ready srgnal from

FDD changed state

When the FDC completes the Seek com-

(Seek End)

mand, this flag IS set lo 1 (high).

If a fault srgnal IS received

from the FDD, or

(Equipment Check)

if the track 0 srgnal fails to occur after 77

step pulses (Recalibrate Command) then

this flag is set

When the FDD IS in the not-ready state and

(Not Ready)

a Read or Write command IS Issued, this

flag IS set If a Read or Write command is

issued to side 1 of a single-sided drive,

then this flag IS set

This flag IS used to indicate

the state of the

(Head Address)

US:

(Unit Select 1)

Us0

head at interrupt.

This flag IS used to indicate

a drive unit

number at interrupt.

This flaa is used to Indicate a drive unit

(Unit Select 0)

Status Register 1

(End of Cylinder)

number at

interrupt

When the FDC tries to access a sector be-

yond the final sector of a cylinder,

this flag

set

Not used. This bit is always 0 (low)

DE(Data

Error)

When the FDC detects a CRC(1) error in ei-

ther the ID field or the data field, this flag is

set

(Overrun)

If the FDC is not serviced by the host sys-

tem during data transfers within a certain

time interval. this flaa is set.

Not used. This bit is alwavs 0 (low).

Table 3. Status Register Identification (cont)

NO.

Name

Status Register 1 (cont)

Function

(No Data)

During execution

of Read Data. Read De-

leted Data Write Data. Write Deleted Data

or Scan command, if the FDC cannot find

the sector specified

in the IDR(2)Register,

this flag is set.

NW(Not Writeable)

(Missing Address

Mark)

During execution of the Read ID command.

if the FDC cannot read the ID field without

an error, then this flag IS set.

During execution of the Read Diagnostic

command. if the starting sector cannot be

found, then this flag is set.

During execution of Write Data, Write De-

leted Data or Write ID command. if the FDC

detect: a write protect srgnal from the

FDD. then this flag is Set

This bit is set if the FDC does not detect the

IDAM before 2 index pulses It is also set if

the FDC cannot find the DAM or DDAM af-

ter the IDAM i s found. MD bit of ST2 is also

Status Register 2

ser at this time.

Not used. This bit IS alwavs 0 (low)

(Control Mark)

During execution

of the Read Data or Scan

command, if the FDC encounters a sector

which contains a deleted data address

mark, this flag is set Also set if DAM is

found during Read Deleted Data

If the FDC detects a CRC error in the data

(Data Error in

field then this flag is set

Data Field)

(Wrong Cylinder)

This bit IS related to the ND bit, and when

the contents of C(3) on the medium is dif-

ferent from that stored in the IDR. this flag

is set

(Scan Equal Hit)

During execution

of the Scan command. if

the condition of “equal” is satisfied,

this

flag is set.

During execution

of the Scan command, if

(Scan Not Satisfied)

the FD cannot find a sector on the cylin-

der which meets the condition. then Cthis

flag is set

(Bad Cylinder)

This bit is related to the ND bit. and when

the contents of C on the medium is differ-

ent from that stored in the IDR and the con-

tents of C IS FFH. then this flag IS set

When data IS read from the medium, if the

(Missing Address

FDC cannot find a data address mark or

Mark in Data Field)

deleted data address mark, then this flag

is set

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