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HP
27130B
Receive Character Processing
The receive interrupt processor is capable of offloading many of the functions usually found in the
host computer. This allows more time for the host CPU to perform other functions.
The order of
processing each received character is as follows:
1.
If the received character has an error condition, and the "ignore parity error
ll
bit is set in the
Write Card Configuration, Subfunction 13 (WCC, SF 13), the parity error condition is cleared.
2.
It
there still is an error after step 1) and the lIignore all errors" bit is set in \VCC, SF 13, the
character is discarded. Otherwise, the current receive record is marked "bad". If enabled by WCC,
SF 31, the record is then made available for the host, or a substitute character is fetched to
replace the bad one and processing continues.
3. If the character is a handshake character, and handshaking is enabled, check the character for an
ACK if ENQ/ ACK is enabled, or for X -ON or X -OFF if X -ON/X -OFF is enabled.
If
so, process
the character and discard it.
4. If the character is a signal character, and signal character detection is enabled, generate the ap-
propriate event and discard the character.
5. If the character is quotable, and quoting is enabled, check the previous character for the quoting
character. If the quoting character is present, replace it with the received character, and skip the
edit and terminating condition checks.
6. If the character is an edit character, and edit mode is enabled, check for backspace or line delete,
and perform the edit function.
7. If the character is a single text terminator, and single text termination is enabled, terminate the
record and make it available to the host. If termination stripping is disabled, add the character to
the buffer.
If the received character does not match any conditions described in steps 1 through 7, the character
now is added to the current record.
8. If the end -on -count option is enabled, a check against the end -on -count is made. If the count is
exhausted, the current record is terminated with an "end-on-count
ll
termination.
9. If the internal card end-on-count is reached, terminate the record.
10. If
the Alert 1 mode is enabled, generate an event to notify the host that at least one character
has been received, if this has not already been done for this record.
The order of processing the received character listed in steps 1 through lOis the precedence imple-
mented by the MUX firmware. Only one type of termination is assigned to each receive record.
The following descriptions frequently use the term IIcurrent receive record". The "current receive
record" is the currently active record that can receive data from the device. If the current receive
record does not exist, a record is created and the character, or the termination condition, is added to
the record.
Note that a condition may cause the generation of a record which contains no "data
ll
(for example,
Carriage Return (CR) is not data, it is line protocol). You should be aware that the text record may be
of zero length. In this case, you will be notified of the condition that caused the termination in the
request status block.
4-4
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