Software Checking - HP 7470A Interfacing And Programming Manual

0 Xon Trigger Character — This specifies the character string the
plotter will use to signal the computer that there is sufficient space in
the buffer to resume sending data. The DC1 character (decimal
equivalent 17)is generally used for the Xon trigger.
The following discussion of the four handshake methods includes the
pertinent variables and identifies the commands which will establish
their values.
Software Checking
Software checking is a nonautomatic handshake method in which the
user's program repeatedly asks the plotter how many characters of
empty space remain in the buffer. When the plotter response is bigger
than the next block of data, the program will transmit the data block to
the plotter. This method is inefficient in time-share environments.
The advantage of software checking is that it is independent of hard­
ware and operating system abilities required to implement other hand­
shake modes;therefore, it usually makes software transportable between
computer systems. The limitation of this method of handshaking is
that it uses up computer time.
To match the requirements of the computer system, these variables
may be specified for the software checking handshake mode by using
the appropriate command:
0 Turnaround delay (ESC . M command)
0 Output trigger character (ESC . M command)
0 Echo terminate character (ESC . M command)
Output initiator character (ESC . M command)
Output terminator (ESC . M command)
Intercharacter delay (ESC . N command)
RS232-C/CCITT V.24INTERFACING 10-17