DS21FT40 datasheet(2/87 Pages) DALLAS

2 / 87 page

DS21FT40

2 of 87

dual two-frame elastic stores contained in each of the four framers can be independently enabled and

disabled as required. The device fully meets all of the latest E1 specifications including CCITT/ITU

G.704, G.706, G.962, and I.431 as well as ETS 300 011 and ETS 300 233.

Functional Description

The receive side in each framer locates FAS frame and CRC and CAS multiframe boundaries as well as

detects incoming alarms including, carrier loss, loss of synchronization, AIS and Remote Alarm. If

needed, the receive side elastic store can be enabled in order to absorb the phase and frequency

differences between the recovered E1 data stream and an asynchronous backplane clock which is

provided at the RSYSCLK input. The clock applied at the RSYSCLK input can be either a 2.048 MHz

clock or a 1.544 MHz clock. The RSYSCLK can be a burst clock with speeds up to 8.192 MHz.

The transmit side in each

framer is totally independent from the receive side in both the clock

requirements and characteristics. Data off of a backplane can be passed through a transmit side elastic

store if necessary. The transmit formatter will provide the necessary frame/multiframe data overhead for

E1 transmission.

Reader’s Note: This data sheet assumes a particular nomenclature of the E1 operating environment. In

each 125 us frame, there are 32 8–bit timeslots numbered 0 to 31. Timeslot 0 is transmitted first and

received first. These 32 timeslots are also referred to as channels with a numbering scheme of 1 to 32.

Timeslot 0 is identical to channel 1, timeslot 1 is identical to Channel 2, and so on. Each timeslot (or

channel) is made up of 8 bits which are numbered 1 to 8. Bit number 1 is the MSB and is transmitted

first.

Bit number 8 is the LSB and is transmitted last.

Throughout this data sheet, the following

abbreviations will be used:

FAS

Frame Alignment Signal

CAS

Channel Associated Signaling

Multiframe

International bits

CRC4

Cyclical Redundancy Check

CCS

Common Channel Signaling

Additional bits

E-bit

CRC4 Error Bits

DS21FT40 Datasheet(PDF) 2 Page - Dallas Semiconductor