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HP
27130B
TRANSMIT CHARACTER PROCESSING
If either 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 "append output
separator" option in the write device data subfunction code. The output separator text is programmed
by using
wee,
SF 28.
Transmitting Transparent or Binary Data
Transparent, or binary, data are 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 also must be disabled to eliminate those characters from being transmitted
within the user's binary data.
BUFFER FLUSHING
Several control card requests are provided to flush (clear) any receive and transmit records on the card.
The control card request with subfunction 1 or 2 is used to flush the current backplane receive buffer,
and to flush all the queued receive buffers, respectively. The control card request with subfunction 3
is used to flush all the queued transmit buffers.
The current backplane receive buffer is defined to be the record for the next host read. If the S-bit is
set for the host read and if there are any data remaining, the remaining data are the current receive
buffer.
If
the previous read has the S-bit set and there are no remaining data, the current backplane
buffer is defined to be the next record for the host read.
If no buffer exists on the card, the control card request will be ignored.
PROGRAMMING THE RECEIVER AND TRANSMITTER
The selection of the transmission mode is programmed by using the
wee,
SF 5.
Simplex receive and simplex transmit are provided to turn off the transmitter and receiver,
respectively.
The character size for the receiver and the transmitter may be specified at 7 or 8 bits per character,
not including an optional bit for even or odd parity. On transmit, the user data will be processed
byte-by-byte, passing the 7 or 8 least significant bits in each byte to the transmitter, depending on
the programmed character size. A parity bit will be added by the MUX if even or odd parity is en-
abled. On receive, the incoming data will be passed to the user's buffer into the 7 or 8 least significant
bits of each byte, with the unused bits being zeros. The parity bit is never returned to the user. The
character length is programmed by using
wce,
SF 11. The format of an asynchronous message is
shown in Figure 4-1.
The baud rate and the number of stop bits are programmed by uSIng the
wec,
SF 10 and 12,
respectively.
4-12
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