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PEF 81912/81913
Functional Description
Data Sheet
57
2001-03-30
1. Local D-Channel Controller Transmits Upstream
In the initial state (’Ready’ state) neither the local D-channel sources nor any of the
terminals connected to the S-bus transmit in the D-channel.
The Q-SMINT
IX S-transceiver thus receives BAC = “1” (IOM
-2 DU line) and transmits
S/G = “1” (IOM
-2 DD line). The access will then be established according to the
following procedure:
Local D-channel source verifies that BAC bit is set to ONE (currently no bus access).
Local D-channel source issues TIC bus address and verifies that no controller with
higher priority requests transmission (TIC bus access must always be performed even
if no other D-channel sources are connected to IOM
-2).
Local D-channel source issues BAC = “0” to block other sources on IOM
-2 and to
announce D-channel access.
Q-SMINT
IX S-transceiver pulls S/G bit to ZERO (’Local Access’ state) as soon as
CNT
≥
n (see note) to allow sending D-channel data from the entitled source.
Q-SMINT
IX S-transceiver transmits inverted echo channel (E bits) on the S-bus to
block all connected S-bus terminals (E = D).
Local D-channel source commences with D data transmission on IOM
-2 as long as
it receives S/G = “0”.
After D-channel data transmission is completed the controller sets the BAC bit to
ONE.
Q-SMINT
IX S-transceiver transmits non-inverted echo (E = D).
Q-SMINT
IX S-transceiver pulls S/G bit to ONE (’Ready’ state) to block the D-channel
controller on IOM
-2.
Note: If right after D-data transmission the D-channel arbiter goes to state ’Ready’ and
the local D-channel source wants to transmit again, then it may happen that the
leading ’0’ of the start flag is written into the D-channel before the D-channel
source recognizes that the S/G bit is pulled to ’1’ and stops transmission. In order
to prevent unintended transitions to state ’S-Access’, the additional condition CNT
≥
2 is introduced. As soon as CNT
≥
n, the S/G bit is set to ’0’ and the D-channel
source may start transmission again (if TIC bus is occupied). This allows an equal
access for D-channel sources on IOM
-2 and on the S interface.
2. Terminal Transmits D-Channel Data Upstream
The initial state is identical to that described in the last paragraph. When one of the
connected S-bus terminals needs to transmit in the D-channel, access is established
according to the following procedure:
S-transceiver recognizes that the D-channel on the S-bus is active via D = ’0’.
S-transceiver transfers S-bus D-channel data transparently through to the upstream
IOM
-2 bus.