Tandy 1000 SL Technical Reference Manual page 199

ter 3 contains the drive status information stored inter-
nally in FDC registers.
Invalid
If an Invalid command is sent to the FDC (a command
not defined above), then the FDC will terminate the com-
mand after bits 7 and 6 of status register 0 are set to 1
and 0, respectively. No interrupt is generated by the
pPD765AIpPD7265 during this condition. Bits 6 and 7
(DIO and RQM) in the main status register are both 1
(high), indicating to the processor that the pPD765AI
pPD7265 is in the result phase and the contents of sta-
tus register 0 (STO) must be read. When the processor
figure 5. Data format (Sheet 1 of 2)
GAP4a SYNC
FF
W
reads status register 0 it will find an 80H, indicating an
Invalid command was received.
A Sense Interrupt Status command must be sent after a
seek
or
recalibrate interrupt, otherwise the FDC
will
consider the next command to be an Invalid command.
In some applications the user may wish to use this com-
mand as a No-Op command to place the FDC in a
standby or no operation state.
DATA C GAP3 GAP4b
m g m
IAM GAP1 SVNC IDAM
t
~
;
I
FC FF
M
FE L
GAP2 SYNC DATAAM
111 6. FF W FBoiFB
26. 6.
Data
Format
Figure 5 shows the data transfer format for thepPD765A
and pPD7265 in various modes.
GAP1 SYNC IDAM
161
6 .
FF
W
FE
I
pP0765A [FM Model
DATA C QAP3 GAP4
m
; m
C
;
I
i
GAP? SYNC DATAAY
111 6x FBorF8
FF W
L
* d e .
I
Fmpe.1 N Tim..
- 1
pP07265 [FM
Mode]
Index R l p a N T i m . I
~ P 0 7 6 5 A [MFM Mode]
I
-1 N
nm.
I
pPD7265 [MFM Mode]
IDAM
6-24