DS26401 datasheet(189/309 Pages) DALLAS

189 / 309 page

DS26401 Octal T1/E1/J1 Framer

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10.13 Receive Elastic Stores Operation

The DS26401 contains dual two-frame elastic stores, one for the receive direction, and one for the transmit

direction. Both elastic stores are fully independent. The transmit and receive side elastic stores can be

enabled/disabled independent of each other. Also, each elastic store can interface to either a 1.544MHz or

2.048/4.096/8.192/16.384MHz backplane without regard to the backplane rate of the other elastic store.

The elastic stores have two main purposes. First, they can be used for rate conversion. When the DS26401 is in

the T1 mode, the elastic stores can rate convert the T1 data stream to a 2.048MHz backplane. In E1 mode, the

elastic store can rate convert the E1 data stream to a 1.544MHz backplane. Secondly, they can be used to absorb

the differences in frequency and phase between the T1 or E1 data stream and an asynchronous (i.e., not locked)

backplane clock (which can be 1.544MHz or 2.048MHz). In this mode, the elastic stores will manage the rate

difference and perform controlled slips, deleting or repeating frames of data in order to manage the difference

between the network and the backplane.

If the elastic store is enabled, then either CAS or CRC4 multiframe boundaries will be indicated via the RMSYNC

output as controlled by the RSMS2 control bit (RIOCR.1). If the user selects to apply a 1.544 MHz clock to the

RSYSCLK pin, then the RBCS registers will determine which channels of the received E1 data stream will be

deleted. In this mode an F-bit location is inserted into the RSER data and set to one. Also, in 1.544 MHz

applications, the RCHBLK output will not be active in Channels 25 through 32 (or in other words, RCBR4 is not

active). If the two-frame elastic buffer either fills or empties, a controlled slip will occur. If the buffer empties, then a

full frame of data will be repeated at RSER and the RLS4.5 and RLS4.6 bits will be set to a one. If the buffer fills,

then a full frame of data will be deleted and the RLS4.5 and RLS4.7 bits will be set to a one.

The elastic stores can also be used to multiplex T1 or E1 data streams into higher backplane rates. This is the

Interleave Bus Option (IBO) which is discussed in Section 10.17.

DS26401 Datasheet(PDF) 189 Page - Dallas Semiconductor