Tandy 1400LT Service Manual page 292

Status
Register Identification
Pin
No. Name Function
Status Register 0
D7, IC D7=0 and D 6 = 0
D, (Interrupt Normal termination of command,
Code) (NT).
Command was completed and properly
execulted.
D,=O and D,=I
Abnormal termination of command,
(AT).
Execution of command was started but
was not successfully completed.
D , = l and D6=0
Invalid command issue, (IC).
Command which was issued was never
started.
D , = l and D,=l
Abnormal termination because during
command execution the ready signal
from FDD changed state.
D, SE
When the F D C completes the Seek
(Seek End) command, this flag is set to 1 (high).
D, EC
If a fault signal is received from the
(Equipment
Check)
FDD, or if the track 0 signal falls to
occur after 77 step pulses (Recalibrate
Command) then this flag is set.
D, N R
When the F D D is in the not-ready
state and 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.
(Not Ready)
D, HD (Head This flag is used to indicate the state
of the head at interrupt.
Address)
D, US, (Unit This flag is used to indicate a drive
unit number at interrupt.
This flag is used to indicate a drive
unit number at interrupt.
Select
1)
Do US, (Unit
Select 0)
~ ~
Pin
No. Name Function
Status Register 1
D,
E N (End of When the F D C tries to access a sector
beyond the final sector of a cylinder,
this flag is set.
Cylinder)
D 6
D, D E When the F D C detects a CRC(1)
Not used. This bit is always 0 (low).
error in either the ID field or the data
field, this flag is set.
(Data Error)
D, OR
If the F D C is not serviced by the host
system during data transfers within a
certain time interval, this flag is set.
(Overrun)
D,
Not used. This bit is always 0 (low).
D,
N D During execution of Read Data. Write
Deleted Data or Scan command, if the
F D C cannot find the sector specified
in the IDR(2) Register, this flag is set.
(No Data)
During execution of the Read I D
command, if the FDC cannot read the
ID field without an error, then this
flag is set.
During execution of the Read A
Cylinder command, if the starting
sector cannot be found, then this flag
is set.
DI
NW (Not During execution of Write Data, Write
Writable) Deleted Data or Format A Cylinder
command, if the F D C detects a write
protect signal from the FDD, then this
flag is set.
Do MA (Missing If the F D C cannot detect the data
Address
Mark)
address mark or deleted data address
mark, this flag is set. Also at the same
time, the M D (missing address mark
in data field) of status register 2 is set.
F-23