Nortel NT1R20, Description

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Description Page 23 of 290
Line cards Description
Peripheral equipment
Peripheral equipment (PE) line cards all have a similar architecture (shown in
Figure 8). The various line cards differ only in the number and types of line
interface units.
Peripheral equipment (PE) line cards are not intelligent cards, but rather must
work in conjunction with a QPC659 Dual-Loop Peripheral Buffer Card (see
Figure 5). The peripheral buffer card generates two sets of “card select”
signals. A separate card enable signal is generated for each card slot in the PE
backplane. A four-bit encoded line address is used to select an individual line
interface unit upon that card (see Table 3).
The peripheral buffer card maintains a table of which line card and line unit
address is assigned to a particular timeslot in the SL-1 network loop. It uses
that information to generate the card enable and line address signals at the
proper time.
A line unit is enabled by the simultaneous occurrence of a card enable signal
for the card that it resides on and a line address that corresponds to the address
of the line unit appearing on the line address bus. When these conditions
occur, the data that is present on the SL-1 network loop at that time is written
to and read from the line unit codec.