Tandy 1000 SL Technical Reference Manual page 186

NEC
Table 3. status Register Identification
Table 3. Status Resister Identification (contl
Pln
no.
lknw r u n c t l o n
Pln
Yo. lknr runctlon
Status Register
0
D73
D6
IC D7=0 and
D6=O
(Interrupt Code) Normal termination
of
command, (NT).
Command was completed and properly ex-
ecuted.
Abnormal termination
of
command, (AT).
Execution of command was started but
was not successfultv completed.
D7 = O and Dg=l
D7 = 1 and Dg=O
Invalid command issue, (IC). Command
which was issued was never started.
D7=landDg=l
Abnormal termination because during
command execution the ready signal from
FDD changed state.
D5
SE When the FDC completes the Seek com-
mand. this flag is set to 1 (high).
D4
EC Ifafaultsignal is receivedfromthe FOD. or
if the track
0
signal fails to occur after 77
step pulses (Recalibrate Command) then
this flag is set.
When the FDD 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.
This flag is used to indicate the State
of
the
This flag is used to indicate a drive unit
number at interrupt.
This flag is used to indicate a drive unit
number at interruDt
(Seek End)
(Equipment Check)
D3
NR
(Not Ready)
Dp
HD
D1
us1
Do US0
(Head Address) head at interrupt.
(Unit Select 1)
(Unit Select
OI
Status Register 1
D7 EN
When the FDC tries to access a sector be-
yond the final sector of a cylinder, this flag
is set
(End of Cylinder)
D6
Dg
DE
Not used. This bit is always 0 (low).
When the FDC detects a CRC(1) error in ei-
(Data Error) thertheiDfieldorlhedatafield,thisflagis
set.
If the FDC is not serviced by the host sys-
tem during data transfers within a certain
time interval. this llaa is set.
Dq OR
(Overrun)
D3
Not used. This bit is always 0 (low).
Status Reoitter 1 Icontl
Dp ND During execution of Read Data. Write De-
leted Data or Scan command, if the FDC
cannot find the sector specified in the
(No Data)
IDR(2) Register, this flag is set.
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 A Cylinder
command, if the starting sector cannot be
found, then this flag is set.
D1 NW During execution of Write Data. Write De-
leted Data or Format A Cylinder command,
if the FDC detects a write protect signal
from the FDD, then this flag is set.
Do MA If the FDC cannot detect the data address
mark or deleted data address mark, this
flag is set. Also at the same time. the MD
(missing address mark in data field) of
status register 2 is set.
D7 Not used. This bit is always 0 (low).
06 CM 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.
if the FOC detects a CRC error in the data
field then this flag is set.
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 IDA. this flag
is set
(Not Writable)
(Missing Address
Mark)
Status
Register 2
(Control Mark)
D5
DD
(Data Error in
Data Field)
(Wrong Cylinder)
D4
WC
Dg
SH During execution of the Scan command, if
the condition of "equal" is satisfied, this
flao is set
(Scan Equal Hit)
Dp SN During execution of the Scan command, if
the FDC cannot find a sector on the cylin-
der which meets the condition, then this
flag is set.
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
FDC cannot find a data address mark or
deleted data address mark, then this flag
is set.
(Scan Not Satisfied)
D1 BC
(Bad Cylinder)
Do MD
(Missing Address
Mark in Data Field)
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