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HP 27130A
To prevent any deadlock situation, the MUX will transmit the X -ON character even if the device had
sent an X -OFF character as part of the device X -ON/X -OFF handshake.
Single Text Termination
For single text termination, you have the option of determining which characters are to be used
as the text terminator. An example of a single text terminator is the carriage-return character
(CR,
~OH).
The single text terminator is not added to the buffer unless enabled by WCC, SF 8. The
character is returned in the event status block and the request status block.
The Single Text Termination option is enabled by setting the End On Single Text Terminator op-
tion in the read device data subfunction code or in the data block of the WCC, SF 1. This op-
tion may also be toggled (on/off) for the duration of the read device data request by setting the "tog-
gle STT II bit in the request subfunction.
The single text terminator characters are programmed by specifying the actual ASCII characters by
using the WCC, SF 32. A maximum of eight characters per port may be designated as text terminators
at any time.
End-On-CountText Termination
The End-On-Count Text Termination option is enabled by setting the End-On-Count option in the
read device data subfunction code or in the data block of the WCC, SF 1. The count is programmed
by using the WCC, SF 2. When the count decrements to zero, the current receive record will be
terminated with the message type indicating an end -on -count.
The End-On-Count option should not be confused with the internal card end-on-count which is
set by the MUX firmware to 252 bytes. This internal count is used to manage the receive buffers on
the card. When this count is exhausted, the current record will be terminated and will be made
available to the host.
The termination type will be set to IImessage terminated by the card, more
data coming". This procedure allows the host to start reading data from the card while the card
is still receiving data from the device.
Alert 1 Mode
When this mode is enabled, and if there is no read device data request pending on the card, and
if none of the conditions discussed above were encountered to terminate the record, the firmware
will notify the host by a IIdata available" event that at least one character was received. The host
should post a read device data request upon receiving this notification. The card will return all
characters received from the time that the alert event status was posted up to the execution of the
read. The read buffer must be large enough to hold the maximum number of characters;
otherwise, data will be discarded unless the S-bit is set.
If any of the text termination options discussed above are enabled, they may terminate the
record early and the host will receive that text termination code and not the alert code for the mes-
sage type.
If the alert 1 read mode is enabled and the host posts a read device data request, the card will not
suspend the read when no data is available
on
the
I/O
channel-to-card
interface module
4-9
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