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HP 27130A
The preceding note has several implications. If the next read request exceeds the remaInIng data
length, the read will be terminated early with the above termination code. Note that the read
request length in this case will not be satisfied. If the read request length is less than the remaining
data length, the read will be satisfied in total. If the S-bit is set, any data remaining will be saved
for future read requests.
If the frontplane has no active receive read, or if the frontplane receive record is less than the read
request length, the firmware will set the down -counter to the remaining count needed to satisfy the
read.
The firmware will suspend the read request until the receive record is available for the
backplane (i.e., until either the down -counter hits zero, or a terminating condition is detected).
If a read request is terminated by the down-counter hitting zero, the termination code for the
record is "card terminated read, no more data".
Host Initiated Text Termination
There are many occasions when the host would like to terminate data transfer early without
losing what ,has already been read. For example, an application may require the read to be terminated
by satisfying the length, or by timing out.
A control card request with subfunction 4 allows the host to terminate the front plane receive
record with the "host initiated text termination" termination code. If no read request is active, a
receive record will be' generated and it mayor may not contain any data. However, no record is
generated if there is no buffer space.
TRANSMIT CHARACTER PROCESSING
If
echoing or software handshaking is enabled, the transmit interrupt processor will give priority
to those characters before transmitting any user data. However, if a current transmit record is active,
the echoing will be delayed until the current record is empty. See the paragraph "Type Ahead and
Echoing" for additional details.
Automatic Output Separators Appendage
The firmware will append one or two characters to the transmitted message depending upon the
write option. The Automatic Output Separators Appendage option is enabled by setting the "ap-
pend output separator" option in the write device data subfunction code. The output separator text
is programmed by using WCC, SF 28.
Transmitting Transparent or Binary Data
Transparent, or binary, data, is defined to be data written with no processing by the firmware. This
may be achieved by disabling options
such
as
Automatic
Output
Separators
Appendage.
Furthermore, software handshaking must also be disabled to eliminate those characters from
being transmitted within the user's binary data.
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