HP 7470A Interfacing And Programming Manual page 172

no enquiry character or acknowledgment string. If, however, the com­
puter is configured to send an ENQ anytime it is ready to send data to
the plotter, the plotter will automatically respond with ACK when it
receives ENQ. This "dummy handshake" is not dependent upon avail­
able buffer space and does not protect against buffer overflow.
EXPLANATIONThe two instructions, ESC .I and ESC. H, are mu­
tually exclusive. With handshake mode 2, the only parameter of the
ESC . M command used when responding to the enquiry or Xon trigger
character is the turnaround delay. Refer to the chart under the ESC . H
instruction to see which parameters are used in various plotter output
situations. Choose your mode using ESC . I or ESC . H, depending on
the requirements of your system.
The parameters for both ESC . H and ESC . I are the same and are
described below, first as interpreted for the enquire/ acknowledge hand­
shake and then as interpreted for the Xon—Xoff handshake.
For Enquire/Acknowledge Handshake
<DEC> This first parameter specifiesthe block size; it is evalu­
ated modulo 256. Default block size set when the parame­
ter is omitted is 80 bytes.
<ASC> This parameter sets the enquiry character. The para­
meter may be the decimal equivalent of any ASCII
character in the range 0 to 127. If the parameter is
omitted, it assumes the default value 0 (NULL charac­
ter) disabling enquire/acknowledge handshake. Any
value other than 0 enables enquire/ acknowledge hand­
shake. However, the value 5 (enquire character, ENQ) is
generally used.
<ASC> . . . <ASC> This is a list of 1 to 10 parameters, separated by
semicolons,which specifythe acknowledgment string.
Decimal equivalents of ASCII characters 0 to 127 are
valid. The value 0 is not transmitted and will terminate
the string. The value 6 (acknowledge character, ACK) is
generally used. If the parameter is omitted, it assumes
its default value and no characters are sent.
For Xon—Xoff H andshake
<DEC> This first parameter sets the Xoff threshold level by
specifying the number of empty bytes remaining in the
buffer when the Xoff character is to be sent. The practi­
cal range is 10 to 254. If the Xoff parameter is specified
to be greater than 128 (half the buffer size), the Xon
threshold level will be reset (from its automatic setting
of half the buffer size) so that the Xon character will be
sent when one byte more than the Xofflevel is available.
10-30 RS-232-C/CCITT V24 INTERFACING