X25AM Programming Manual

ITI Applications
X25AM Programming Manual—527201-001
2-17
Data Packetizing by ITI
All four values can be changed with SETMODE 9, which overrides the default value.
SETMODE 38 alters the current value and processing for the line-termination
character. Any mix of four default and application-defined interrupt characters is
possible. There is no optional specification of interrupts for 6510 terminals in
conversation mode. All interrupt characters are carriage returns (CR).
ITI uses these specifications to determine which PAD parameter 3 value should be
sent to the PAD as follows:
•
If all four interrupt characters are defined as CR, then parameter 3 value 2 is
transmitted to the PAD.
•
If all four interrupt characters are not defined as CR, then parameter 3 value 126 is
transmitted to the PAD.
Data Forwarding and the Break Signal
A break signal is transmitted from the terminal when the BREAK key is pressed.
The PAD responds to the break signal by generating an interrupt packet with an
indication of break message and discards any data that it is holding. Interrupt packets
take priority in the network. When ITI receives an interrupt packet, it terminates the
READ operation with error 111 (BREAK occurred on this request). No data is
transferred to the application process. Therefore, some data may be lost.
A detailed explanation of application break handling can be found in the Guardian
Programmer’s Guide.
Data Packetizing by ITI
ITI segments data from the application into blocks of either 256 bytes or
PAGE6520BLKSIZE. Each block is packetized as specified by the modifier
PACKETSIZE or a SETMODE 31 (parameter value must be less than PACKETSIZE).
ITI can send up to L3WINDOW packets before it requires an acknowledgement for the
first packet. If no acknowledgement occurs then a timeout occurs, followed by a retry
operation. Based on the type of response, the entire buffer may be retransmitted.
Table 2-5. Default Interrupt Characters
Function Octal Code Character Control Key
Backspace %10 BS CTRL-H
Line Cancel %30 CAN CTRL-X
Line Termination %15 CR CTRL-M
End of File %31 EOF CTRL-Y