XRT83L38 Datasheet, PDF (71/91 Pages) Exar Corporation – OCTAL T1/E1/J1 LH/SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR

XRT83L38
OCTAL T1/E1/J1 LH/SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR
REV. 1.0.0
CLOCK SELECT REGISTER
The input clock source is used to generate all the necessary clock references internally to the LIU. The
microprocessor timing is derived from a PLL output which is chosen by programming the Clock Select Bits and
the Master Clock Rate in register 0x81h. Therefore, if the clock selection bits or the MCLRATE bit are being
programmed, the frequency of the PLL output will be adjusted accordingly. During this adjustment, it is
important to "Not" write to any other bit location within the same register while selecting the input/output clock
frequency. For best results, register 0x81h can be broken down into two sub-registers with the MSB being bits
D[7:3] and the LSB being bits D[2:0] as shown in Figure 25. Note: Bit D[7] is a reserved bit.
FIGURE 25. REGISTER 0X81H SUB REGISTERS
MSB
LSB
D7
D6
D5
D4
D3
D2
D1
D0
Clock Selection Bits
ExLOS, ICT
Programming Examples:
Example 1: Changing bits D[7:3]
If bits D[7:3] are the only values within the register that will change in a WRITE process, the microprocessor
only needs to initiate ONE write operation.
Example 2: Changing bits D[2:0]
If bits D[2:0] are the only values within the register that will change in a WRITE process, the microprocessor
only needs to initiate ONE write operation.
Example 3: Changing bits within the MSB and LSB
In this scenario, one must initiate TWO write operations such that the MSB and LSB do not change within ONE
write cycle. It is recommended that the MSB and LSB be treated as two independent sub-registers. One can
either change the clock selection (MSB) and then change bits D[2:0] (LSB) on the SECOND write, or vice-
versa. No order or sequence is necessary.
TABLE 36: MICROPROCESSOR REGISTER #129, BIT DESCRIPTION
REGISTER ADDRESS
10000001
BIT #
NAME
FUNCTION
D7
Reserved
REGISTER
TYPE
RESET
VALUE
R/W
0
67