DS2155 datasheet(168/262 Pages) DALLAS

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DS2156

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24.2 UTOPIA Clock Modes

When the UTOPIA backplane is enabled, the user can select from several clocking modes: full T1/E1,

clear-channel E1, or fractional T1/E1. Because ATM bytes are byte-aligned in the frame, clear-channel

mode is only available in E1 operation. See Table 24-A for the various register configurations. Figure

24-1 shows a simplified diagram of the clock, data, and sync connections between the framer and the

UTOPIA block.

Figure 24-1. UTOPIA Clocking Configurations

24.3 Full T1/E1 Mode and Clear-Channel E1 Mode

In full T1/E1 mode, the framer is programmed to provide a constant clock (RCLK for the receiver and

TCLK for the transmitter) to the UTOPIA block by setting CCR3.4 and CCR3.5 = 1. The framer also

provides frame-sync pulses to the UTOPIA block. The UTOPIA block is programmed to use the clock

and sync signals by setting U_TCR2.1 and U_RCR2.1 = 0. In this mode the UTOPIA block uses the sync

signal to byte align the transmit data stream and locate the F-bit position in T1 operation and TS0 and

TS16 in E1 operation.

In T1 mode, the receive and transmit UTOPIA blocks always use the frame-sync pulse to gap out the F-

bit position.

In E1 mode, the transmit UTOPIA block can be programmed to gap out TS0 and TS16 by setting

U_TCR1.3 = 0, or use the full 256 bits of the frame by setting U_TCR1.3 = 1. Using the full 256 bits of

the frame is referred to as clear-channel mode and is only available in E1 mode. In full E1 mode, the

receive UTOPIA block always uses the frame-sync pulse to gap out TS0 and TS16. In order for the

receive UTOPIA block to operate in clear-channel mode, set U_RCR2.1 = 1 while in full clock mode or

use the fractional mode of operation described in Section 24.4 with all channels selected.

RECEIVE

FRAMER

RECEIVE

UTOPIA BLOCK

RCLK

GAPPED

CLOCK

FRAME SYNC

CLOCK

SYNC

TRANSMIT

FRAMER

TRANSMIT

UTOPIA BLOCK

TCLK

GAPPED

CLOCK

FRAME SYNC

CLOCK

SYNC

TCLK

DATA

CCR3.4

CCR3.5

NETWORK

UTOPIA

BACKPLANE

DS2155 Datasheet(PDF) 168 Page - Dallas Semiconductor

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