HP 7470A Interfacing And Programming Manual page 157

this trigger character." This character is often a DC1 (decimal equiva­
lent 17)or some other nonprinting ASCII character such as LF or CR
or, when using some implementations of BASIC, the ? (decimal
equivalent 63), which does print.
Turnaround Delay — The turnaround delay is the length of time the
plotter will wait after receiving a computer request and the trigger
character, if any, before it responds. The purpose of this time delay is
to delay the plotter's transmission of requested data until the com­
puter is ready to receive and process it. Systems may require either a
turnaround delay or a trigger character, or both.
Output Initiator Character —The output initiator character is a one—
character initiator that is sent by the plotter at the beginning of a
string. The output initiator tells the computer, "This starts my trans­
mission." Some computers which require an output initator expect
the start—of-text c haracter, STX (decimal equivalent 2), as the plotter's
output initiator.
Output Terminator — The output terminator is a one— or two-character
terminator that the computer requires the plotter to send at the end of
each response to a data request; The output terminator tells the
computer, "This completes my transmission." Often, computers expect
the carriage return character, CR (decimal equivalent 13), as the
plotter's output terminator.
Echo Terminate Character — Echoing is commonly found in full
duplex systems. Use of the echo terminate parameter in a device
control command tells the plotter that the computer will echo all
responses and that this echoed data should be ignored (the plotter's
data buffer should be closed) until an echo terminate character is
received. When the plotter receives the echo terminate character, it
reopens the data buffer to receive graphics data from the computer.
Computers often use the line feed character, LF (decimal equiva­
lent 10), as the echo terminator. If the computer does not echo the
peripheral's response, this variable must be zero (equivalent to null)
or must be omitted.
Intercharacter Delay — Some computers cannot process data as fast
as the plotter can transmit it due to limited buffering in the I/O port.
This can be compensated for by delaying each transmission from the
plotter a period of time as specified by the intercharacter delay
variable. This intercharacter delay is added to a turnaround delay (if
one has been specified) before the first character is sent by the
plotter, and is also inserted before each subsequent character in a
string being sent to the computer.
RS-232-C/CCITT V.24INTERFACING 10-15