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PSB 2115
PSF 2115
Functional Description
Semiconductor Group
61
11.97
1. NT 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 IPAC S-transceiver thus receives BAC = “1” (IOM-2 DU line) and transmits
S/G = “0” (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.
Local D-channel source issues BAC = “0” to block other sources on IOM-2 and starts
D-channel transmission.
IPAC 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.
IPAC S-transceiver pulls S/G bit to ONE (’Ready’ state) to block the D-channel
controller on IOM-2.
IPAC S-transceiver transmits non-inverted echo (E = D).
IPAC S-transceiver pulls S/G bit to ZERO (’Idle’ state) as soon as n D-bits = ’1’ are
counted on IOM-2 (see note) to allow for further D-channel access.
Note:
Right after transmission the S/G bit is pulled to ’1’ until n successive D-bits = ’1’
occur on the IOM-2 interface. As soon as n D-bits = ’1’ are seen, the S/G bit is set
to ’0’ and the IPAC D-channel controller may start transmission again. This allows
an equal access for D-channel sources on IOM-2 and on the S interface.
The number n depends on configuration settings (selected priority 8 or 10) and the
condition of the previous transmission, i.e. if an abort was seen (n = 8 or 10,
respectively) or if the last transmission was successful (n = 9 or 11, respectively).
Figure 19
illustrates the signal flow in an intelligent NT and the algorithm of the D-
channel priority handler on IOM-2 implemented in the IPAC.