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F.1
APPENDIX F
Software Handshaking Data
SOFTWARE HANDSHAKE
The Terminal operates at speeds up to 19,200 baud; however,
it
may not be able to keep up with incoming data. Incoming
characters are stored in a 32-character buffer and processed
on a first in/first out basis. When the buffer contents reach
22 characters, the Terminal transmits 13H (XOFF or DC3).
On receipt of this signal,
the
host should suspend its transmis-
sion to the Terminal. Eventually,
if
the host stops transmitting,
the Terminal will deplete the buffer. When 1 O characters re-
main in the buffer, the Terminal will transmit 11 H (XON or
DC1) to signal the host that it may resume transmission. If
the host fails to respond to an XOFF from the Terminal in
a timely manner, the buffer continues to fill. When the 32-char-
acter capacity of the buffer is exceeded, a buffer overflow
will
occur.
To determine if the buffer will overflow, use the
following formula:
Time to respond to XOFF
=
70
I
receiver speed
The value, 70, was obtained from the following formula:
70
=
(buffer length - XOFF point-worst case)* number
of bits
70
=
(32-22-3)* 10
Example
The Z-29 is transmitting and receiving at 9600 baud. The Ter-
minal has just sent an XOFF, which the host must respond
to within 7.29 milliseconds.
Time to respond to XOFF
=
70
I
9600
=
0.00729 sec-
onds
When the buffer overflows, the Z-29 discards the most recent
character in the buffer and places the current character into
the buffer.
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