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HP 27130A
("backplane")
or the MUX -to-device interface module ("frontplane"). Instead, you will receive a
transmission log of zero length.
The alert 1 read mode is enabled by setting the alert 1 bit in the data block of the WCC, SF 3. When
the mode is enabled, and there
is
data on the frontplane, and there is
no
data on the backplane, a
"data available" event will be generated immediately.
In summary, the alert
1 read mode has the following characteristics:
1. If
the backplane has no receive record, an event will be generated when the frontplane
receives a character which does not meet any of the terminating conditions described above.
2. If the backplane has no receive record and the front plane has an active record, the
backplane will cause the frontplane to terminate the record to satisfy the read.
3. If the backplane and the front plane both have no active record, the read will be ter-
minated immediately with a transmission log of zero.
The text terminating code will be alert
1.
Type
Ahead and Echoing
Type ahead mode allows the MUX to receive text before the host has posted a read for the text. The
card has enough RAM space to buffer several text lines. This will allow the device to send many lines
bef ore stopping.
If the receive buffer should become full, any new incoming data will be lost. If echoplex is en-
abled' you will notice this when the typed character is not echoed.
NOTE
If you should change any of the read termination para-
meters, such as text termination, end-on-count, and so
on, the new paramaters will not affect any text record
that has already been terminated. If the front plane has
an active receive record, the text termination conditions
will become active after the current record is ter-
mina ted. Otherwise, the new read parameters will be-
come effective immediately.
In echoplex mode, if a transmit record is active, any incoming characters will be echoed after
the transmit record is empty. This should prevent incoming characters from interrupting anyout-
going escape sequences which are less than or equal to 252 bytes.
It
will not, however, prevent a
write from interrupting an escape sequence being echoed from the receiver, or if software hand-
shaking is enabled, the handshake characters will not be prevented from interrupting any outgo-
ing text.
4-10
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