Tandy 1000 SL Technical Reference Manual page 196

NEC
pPD76bA/7265
tively. Also, the loss of a ready signal at the beginning of
a command execution phase causes bits 7 and 6 of sta-
tus register0 to be set to 0 and 1, respectively.
Table 7 shows the relationship between N, SC, and GPL
for various sector sizes.
Table 7 . Sector Size
8" Standard
Floppy
FM Mode 128 Bytes/Seclor 00 1A 07 1B
256 01 O F
O E
2A
512 02 08 1B 3A
1024 03 04 47 8A
2048 04 02 C8 FF
Fornut
MWMU
n sc
aPi(1)
o#(z,q
4096 05 01 C8 FF
MFM Model4) 256
01 1A
OE
36
512 02 O F 16 54
1024 03 08 35 74
2048 04 04
99 FF
4096 05 02
C8
FF
8192 06 01 C8 FF
5V4"
Minifloppy
FM Mode
128Bytes/Sector 00
12
07
09
128
00
10 10 19
256 01 08 18 30
512 02 04 46 87
1024 03 02 C8 FF
2048 04 01 C8 FF
MFM Mode(4) 256 01 12 O A OC
256 01 10 20 32
512 02 08 2A 50
1024 03 04 80 F O
2048 04 02 C8 FF
4096 05 01 C8 FF
31h"
Sony
Mlcm Floppydirk
FM Mode 128ByteslSector 0 OF 07 1B
256 1 09
O E
2A
512 2 05 1B 3A
MFM Mode(4) 256 1 OF OE
36
512 2 09 18 54
1024 3 05 35 74
Note:
(1) Suggested values of GPL in Read or Write commands to avoid
(2) Suggested values of GPL in format command.
(3) A l l values except sector size are hexidecimal.
(4) In MFM mode FDC cannot perform a ReadlWritelFormat operation
splice point between data field and ID field of contiguous sections.
with 128 byteslsector. (N =W).
Scan Commands
The Scan commands allow data which is being read
from the diskette to be compared against data which is
being supplied from the main system. The FDC com-
pares the data on a byte-by-byte basis and looks for a
sector of data which meets the conditions of
DFDD
=
Dprocessor, DFDD
<
Dprocessor, or DFDD
>
Dprocessor. The hexidecimal byte of FF either from
memory or from FDD can be used as a mask byte be-
cause it always meets the condition of the comparison.
One's complement arithmetic is used for comparison
(FF
=
largest number, Do
=
smallest number). After a
whole sector of data is compared, if the conditions are
not met, the sector number is incremented (R
+
STP
-
R), and the scan operation iscontinued. The scan opera-
tion continues until one of the following conditions oc-
cur: the conditions for scan are met (equal, low, or high),
thelast sectoron thetrackisreached(ECTT),orthetermi-
nal count signal is received.
If the conditions for scan are met, then the FDC sets the
SH (scan hit) flag of status register2 to a 1 (high) and ter-
minates the Scan command. If the conditions for scan
are not met between the starting sector (as specified by
R) and the last sector on the cylinder ( E m , then the
FDC sets the SN (scan not satisfied) flag of status regis-
ter 2 to a1 (high) and terminates the Scan command. The
receipt of a terminal count signal from the processor or
DMA controller during the scan operation will cause the
FDC to complete the comparison of the particular byte
which is in process and then to terminate thecommand.
Table 8 shows the status of bits SH and SN under vari-
ous conditions of Scan.
Table 8. Scan Conditions
Scan
High
or
0 1
DFDO
=
DPmcessor
Equal
0 0 DFW>
Dprocessor
1 0
Dmn<
If the FDC encounters a deleted data address mark on
one of the sectors (and SK = 0), then it regards the sec-
tor as the last sector on the cylinder, sets the CM (con-
trol mark) flag of status register 2 to a 1 (high) and
terminates the command. If SK=1, the FDC skips the
sector with the deleted address mark and reads the next
sector. In the second case (SK
=
l), the FDC sets the CM
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