Enquire/Acknowledge Handshake - HP 7470A Interfacing And Programming Manual

maximum number of bytes sent by an output statement to allow
room for the overshoot.
Once the Xoff trigger character has been sent, when the amount of
stored data drops to the Xon threshold level, the plotter sends the
Xon trigger character to signal the computer to resume sending
data. The Xon threshold level is automatically set at 128bytes. If the
Xoff threshold level is greater than 128,the Xon threshold is reset to
send the Xon character when one more byte than required by the
Xoffthreshold is available in the plotter's buffer.
Data is again stored in the buffer until all the data are transferred or
until the Xoff threshold level is exceeded again.
The following conditions can be specified for the Xon-flXoff handshake
mode to match the requirements of the computer system, by using the
appropriate command:
Xoff threshold level (ESC . I command)
Xon trigger character (ESC . I command)
Xofftrigger character (ESC . N command)
Intercharacter delay (ESC . N command)
The enquiry character (ESC . I command) must either be defaulted or
specified as zero.
Enquire/Acknowledge Handshake
With the enquire/acknowledge handshake, the computer's operating
system or application program initiates the data exchange process by
querying the plotter about the availability of buffer space. The format
of the exchange is dependent upon the requirements of the computer.
The following conditions can be specified for the enquire/ acknowledge
handshake mode by using the appropriate command:
Turnaround delay (ESC . M command)
Output trigger character (ESC . M command)
Echo terminate character (ESC . M command)
Output initiator character (ESC . M command)
Output terminator (ESC . M command)
Intercharacter delay (ESC . N command)
Immediate response string (ESC . N command)
Data block size (ESC . I or ESC . H command)
10-20 RS-232~C/CCITTv.24 INTERFACING