C04MUNICATIONS
SECTION 6.6
6,6,7
VER.V09F
Data Character
The data characters may consist of any 7 bit pattern with the
exception of the handshake characters : ACK (06 Decimal), NAK
( 15H) and WACK ( 1 3H ),
Checksum
The checksum is formed as the modulo 256 addition of all data
characters, with parity reset, The number formed is transmitted
in ASCII as three decimal digits, Leading zeros are not
suppressed, The most significant digit is sent first.
Insufficient Data Characters
If there are less than 64 characters for the data block, then
the remainder of the block is filled with NULLS (00 Decimal),
The characters are ignored on reception,
Handshaking
Each block of data must be acknowledged by the receiving device,
After a successful reception and if the receiver is ready to
receive another block, then it returns an ACK (06 Decimal),
If
the transfer is deemed unsuccessful for any of the following
reasons:-
1) parity fault on any character
2) Incorrect start or end characters
3) wrong number of character.s
4) checksum error
5) timeout (waiting for characters for 4 sees)
then a failure is returned as a NAK (21 Decimal),
If the receiver accepts the block, but is not ready for further
data, then a wait acknowledge WACK (19 Decimal) character
delaying the transmitter's time out is transmitted, Further
delays can be accumulated by transmitting WACK's at the rate of
one every 2 sees, The message is finally accepted with an ACK.
COMMUNICATIONS FAIWRE
If a failure occurs on transmission and a timeout activates,
then HUNTER will display 'Communications Failure' on the top
line of the display, This message may be overriden by pressing
'X' on the keyboard, This will force transmission for ETX/ ACK
or XON/XOFF; in the case of ACK/NAK then the buffer will be sent
another three times,
A timeout can tie prevented from occurring after a transmission
failure by re-initialising the communications,
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