Table of Contents
Advertisement
HP 27130A
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
ll
•
The "current
receive record
ll
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" (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.
The host may post a read request to the card even when no receive data is available. The card will
suspend the read request until a record is received. If no read request is pending, and the card has a
record available for the host, an asynchronous event, if enabled, is sent to the host to start the read.
See the paragraph "Asynchronous Event" for additional details.
Receive Error Conditions
The firmware will terminate the current receive record when any error condition is sensed. If
the "Do Not Terminate On Error" option is set, the firmware will not terminate the record.
Instead, a user specified replacement character will replace the bad incoming character, see the
"Additional Options" paragraph for further details.
The firmware also has the option of ignoring parity errors (process the character as if the error
did not exist), or to discard characters with any kind of error.
These errors include parity error, framing error, and data overrun.
Signal Character
When the Signal Character option is enabled, every received character is checked for a match
to one of the four signal characters, which are programmable by the user. If a match occurs, the
firmware will generate the appropriate status event.
The signal character is very similar to the use of the BREAK key on a terminal, except that you can
specify any character for this function. For example, the EM character (control-Y) may be used to
interrupt a program from a terminal.
If fewer than four signal characters are desired, the unused characters should be programmed as
duplicates of a lower-numbered used character.
The search for a matching signal character
proceeds from Signal 1 to 4.
4-5
Advertisement
Table of Contents
