Data Sheet
MT8931C
9
with zeros in the B and D-channel and the
activation bit (A-bit) set to zero.
4) As soon as the TE synchronizes to Info2, it
responds with a valid S-Bus frame with data in
the B1, B2 and D-channel (Info3).
5) The NT will then transmit a valid frame with data
in the B1, B2 and D-channel. It will also set the
activation
bit
(A)
synchronization to Info3 is achieved.
to
binary
one
once
If the NT wishes to initiate the activation, steps 2 and
3 are ignored and the NT starts sending Info2. To
initiate a deactivation, either end begins to send
Info0 (Idle line).
D-channel Priority Mechanism
The SNIC contains a hardware priority mechanism
for D-channel contention resolution. All TEs
connected in a point-to-multipoint configuration are
allocated
the
D-channel
approach.
Allocation
accomplished by monitoring the D-echo channel
(E-bit) and incrementing the D-channel priority
counter with every consecutive one echoed back in
using
of
a
D-channel
systematic
the
is
the E bit. Any zero found on the D-echo channel will
reset the priority counter.
There are two classes of priority within the SNIC,
one user accessible and the other being strictly
internal. The user accessible priority selects the
class of operation and has precedence over the
internal priority. The latter (internal priority), will
select the level of priority within each class (i.e., the
internal priority is a subsection of the user accessible
priority). User accessible priority selects the terminal
count as 8/9 or 10/11 consecutive ones on the E-bit
(8 being high priority while 10 being low priority).
The internal priority selects the terminal between 8
or 9 for high class and 10 or 11 for low class. The
first terminal equipment to attain the E-bit priority
count will immediately take control of the D-channel
by sending the opening flag. If more than one
terminal has the same priority, all but one of them will
eventually detect a collision. The TEs that detect a
collision will immediately stop trans-mitting on the D-
channel, generate an interrupt through the Dcoll bit,
reset the DCack bit on the next frame pulse, and
restart the counting process. The remainder of the
packet in the Tx FIFO is ignored.
Figure 8 - Point-to-Point Configuration
Figure 9 - Short Passive Bus Configuration, up to 8 TEs can be supported
Figure 10 - Extended Passive Bus Configuration, up to 8 TEs can be supported
NT
TE
T
R
T
R
0 - 1 Km
NT is operating in adaptive timing
TR is the line termination resistor = 100
NT
TE
T
R
T
R
TE
TE
TE
TE
TE
TE
TE
100 m for 75
impedance cable and 200 m for 150
impedance cable
100 - 200 m
NT is operating in fixed timing
TR is the line termination resistor = 100
0 - 10 m
NT is operating in adaptive timing
TR is the line termination resistor = 100
TE
TE
TE
TE
TE
TE
TE
0 - 10 m
0-500 m
0-50 m
NT
T
R
T
R
TE