7

®

AFE2126

Data is transmitted and received in synchronization with the

48x transmit and receive clocks (tx48xCLK and rx48xCLK).

There are 48-bit times in each baud period. Data In is

received in the first 16 bits of each baud period. The

remaining 32-bit periods are not used for Data In. Data Out

is transmitted during the first 16 bits of the baud period. A

second interpolated value is transmitted in subsequent bits of

the baud period.

txbaudCLK: The transmit data baud rate generated by the

DSP. It is 392kHz for T1 or 584kHz for E1. It may vary from

32kHz (64kbps) to 584kHz (1.168Mbps).

tx48xCLK: The transmit pulse former oversampling sam-

pling clock generated by the DSP. It is 48x the transmit

symbol rate or 28.032MHz for 584kHz symbol rate. This

clock should run continuously.

Data In: This is a 16-bit output data word sent from the DSP

to the AFE. The sixteen bits include tx symbol information

and other control bits, as described below. The data should

be clocked out of the DSP on the falling edge and should be

valid on the rising edge of the tx48xCLK. The AFE2126

reads Data In on the rising edge of the tx48xCLK. The bits

are defined in Table I. Data In is read by the AFE2126

during the first 16 bits periods of each baud period. Only the

first 8 bits are used in the AFE2126. The second 8 bits are

reserved for use in the future products. The remaining 32

bits periods of the baud period are not used for Data In.

Data In Bits

tx Enable Signal—This bit controls the tx Symbol defini-

tion bits. If this bit is 0, only a 0 symbol is transmitted

regardless of the state of the tx Symbol definition bits. If this

bit is 1, the tx Symbol definition bits determine the output

symbol.

tx Symbol Definition—These two bits determine the output

2B1Q symbol transmitted.

FIGURE 4. Receive Timing Diagram.

FIGURE 3. Data In Word.

1

MSB

LSB

23

1

9

Reserved

Loopback

rx Gain

tx Symbol

tx Enable

Data Out

from AFE2126

rx48xCLK

from DSP

rxbaudCLK

from DSP

MSB

Bit 15

LSB

Bit 0

MSB

Bit 15

LSB

Bit 0

Data 1a

Interdata 8 Bits

Data 1

Data 2

Interdata 8 Bits

MSB

Bit 15

4ns

48

1

14

1516

1723

2425

26

39

40

4748

1

4ns

4ns

4ns

t

rx1

A

B

Receive Timing Notes: (1) A baud period consists of 48 periods of the tx48xCLK. (2) The falling edge of the rxbaudCLK

can occur anywhere in area A. The rising edge can occur anywhere in area B. However, neither edge of the

rxbaudCLK can occur within 4ns (on either side) of any rising edge of rx48xCLK. (3) For all data bits after the MSB of

Data 1, the AFE2126 transfers Data Out on the falling edge of the rx48xCLK. The time from the falling edge of

rx48xCLK until Data Out is stable is t

(4) The AFE2126 transfers the MSB of Data 1 on the falling edge of rxbaudCLK. If the falling edge of rxbaudCLK is

synchronized with the falling edge of rx48xCLK, all of the Data Out bits will be the same width. In any case, the time

from the falling edge of rxbaudCLK until the MSB of Data 1 is stable is t

min

9ns

t

rx1

max

14ns