Cc»4MUNICATIONS
SECTION 6.6
6.6
6.6. 1
6.6.2
6.6.3
VER.V09F
ASYNCHRONOUS PROTOCOLS
NOTE: In this section, 'host' means the device communicating
with flUtJTER, whether it be computer, printer, modem or
otherwise.
These protocols may be used by Basic application programs, user
assembly code, CP/M programs or directly in 'Terminal Emulation'
lll)de.
NONE
RECEPTION
As implied, this selection does nothing to control the incoming
data. It behaves as a simple teletype. Characters are placed
into the reception buffer and a calling program may read them
out asynchronously,
TRANSMISSION
Each character is transmitted as the calling program requests it
(except when waiting for the previous character to be sent),
There is no buffering of the output data.
XON/XOFF (DC1 /DC3)
RECEPTION
If an incoming character causes the receive buffer to have 90 or
more unread characters then an XOFF character (DC3,19 Decimal or
Control S) is transmitted, which should prevent the host sending
further characters to HUNTER. When the buffer
is reduced to 10
pending characters, an XON (17 Decimal or Control
Q, DC1) is
transmitted to re-enable the host to HUNTER transmission.
Subsequent XotJs or XOFFs are never transmitted without an
intervening XOFF or XON respectively.
TRANSMISSION
The input data line is also examined for XON or XOFF characters.
If an XOFF or stream of XOFFs are received then transmission
is
stopped as soon as the character being transmitted is finished.
The protocol requires an XON to restart transmission, This
protocol procedure strips 'XON' or 'XOFF' Control characters,
thus returning only valid data,
SLAVE, HUNTER TO HOST TRANSMISSION
TRANSMISSION
It should be noted that following the host transmitting an XOFF,
it is possible, depending on data link speed, to have a further
two characters sent out by HUNTER. This is due to the time
taken to receive the XOFF and the possibility of just missing
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