CCMMUNICATIONS SECTION 6. 7
6.7,2.2
VER.V09F
On transmit, a rising edge (-12V to + 12V) causes a bit to change
on the transmit output (pin 2). On receive, a falling edge
(+12V to -12V) causes the state of the receive input (pin 3) to
be sampled.
It is
important that maximum clock speed on HUNTER should not
exceed 9600 Hz (giving a data rate of 9600 baud), The minimum
speed is approximately 100Hz.
Exceeding this clock rate may cause unpredictable results.
Alternatively, HUNTER can self clock. This is achieved by
selecting from the menu the desired transmit and receive baud
rates
in the range 50-4800 baud, as for asynchronous. On
transmit, the data is sent out by using internal timing, with no
reference to any external clock source.
To receive incoming data HUNTER times from rising edges (-12V
to + 12V) on the receive data line to give internal clocking.
Self clocking
is useful for HUNTER - HUNTER communications. It
may be used over async_hronous modems to provide both increased
throughp~t and data integrity.
Character Synchronisation
To be able to extract eight bit data characters, HUNTER has to
synchronise itself to the incoming characters correctly. This
is done by detecting special synchronising characters called SYN
characters (32H). HUNTER considers synchronisation to have been
achieved after receiving two contiguous SYN characters.
After receiving the two synchronising characters each group of
eight received bits are then considered to be a character.
Synchronisation is considered to have been lost if a line
turnaround character
is received (OFFH). This is equivalent to
an open line.
Prior to sending the synchronising characters,· HUNTER transmits
an OAAH pad character which is to assist in bit synchronisation.
Every data block whether .it consists of one or 500 characters,
must start with a pad character, and two SYN characters and
terminate with line turnaround.
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