HP 9800 SERIES - Page 82

HP-IB Sequence:
ATN
fPOl~DDRSI
Pnmary
Listen
ATN
IPOl~DDRSI
Pflmary
Talk
Status:
ATN
HP 9895A Disc Memory Command Set A-35
As has been seen, the unbuffered read actually uses the
internal buffer to store the data. However, the protocol
used is unbuffered in that the parallel poll response is not
used to indicate when data is available. Thus, there is a
pause in data flow to the HP-IB each time the buffer is
re-filled from
the disc. This pause occurs at the beginning
of the read and after every sector has been transferred.
Depending on when the read is started and the sector inter-
leaving, this pause may be up to 160 milliseconds long.
Unbuffered Read Request
EOJ ATN
P
P
Pll0l000 P 00101
UUUU
1
P
I
POllllll
l
I
Secondary I
D
Opcode
I
E
Unit Unlisten
Send Data Request
ATN
EOJ
P
P
I
Pll00000 I
P P
D
E
Secondary
~ Data Bytes -
No errors.
Sl - 0
Stat 2 - Unchanged
DSJ - 0
Unsuccessful read.
Sl - Error
Stat 2 - Bits A, E and C set, if appropriate.
DSJ -1
ATN
IPlOllllll
Untalk
Requirement for Execution:
See Buffered Read.
Parallel Poll:
The parallel poll response is re-enabled after the operation
is completed, normally or abnormally.
If less than the specified number of bytes is accepted by the
HP-IB controller, the parallel poll response will be re-
enabled by the Untalk command.