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INPUT/OUTPUT FUNCTIONS
25.2 -- Device Dependent I/O Functions
25.2.7 Multiple sector input -- .MREAD, .MERED
The
.MREAD
and
.MERED
functions are both used to read a
multiple number
Or
physically
contiguous
sectors
from
the
diskette
into
a specified buffer.
The .MREAD function will
only return to the calling program iT nc diskette
controller
errors
are
detected
during
the
read attempt.
The.
MERED
function,
on the other
hand,
will
return
to
the
calling
program
IUhether
an
error
occurred
or
not.
The. MERED
runction will return the error status that
was
detected
by
the diskette controller.
If
an
error
occurred,
the
same
type
of
re~overy
procedure described in section 25.2.5
<.DREAD,
. EREAD)
was
attempted.
In
addition,
the same precautions regarding
the
restoring of the read
head
described in that section apply to
the. MREAD
and .
MER ED
~unctions.
ENTRY PARAMETERS:
EXIT CONDITIONS:
B
=
The
logical
unit
number.
are ignored.
Bits
2-7
x
=
The
address
o~
a
seven-byte
I/O
parameter
packet.
The
paT'ameter
packet has the rollowlng rormat:
o
Return status
1
: Starting physical :
sector number
2
to be read
3
Address
o~
multiple
4
sector
bU~Te~
5
6
Number aT
sectors
to be read
The sector bUTTer must be an integral
number
of
sectors in sizel
and must
be large enough
to
accommodate
the
number
of sectors specified in bytes
5 and 6 of the parameter packet.
S~me
as
fo~.DREAD
and
.EREAD~
however,
the
sector buffer contains data rrom
the number of
sectors
specified
in
bytes 5 and 6 Qf the parameter packet
(only if no error occurred).
Page
25-12
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