Preliminary Information

MT9173/74

9-149

Table 6. Status Register

Status

Register

Name

Function

0

SYNC

Synchronization - When set this bit indicates that synchronization to the received

line data sync pattern has been acquired. For DN mode only.

1-2

CHQual

Channel Quality - These bits provide an estimate of the receiver’s margin against

noise. The farther this 2 bit value is from 0 the better the SNR.

3

Rx HK

Housekeeping - This bit is the received housekeeping (HK) bit from the far end.

4-6

Future

Future Functionality. These bits return Logic 1 when read.

7

ID

This bit provides a hardware identifier for the DNIC revision. The MT9173/74 will

return a logic “0” for this bit.

01234567

SYNC

CHQual

Rx HK

Future Functionality

ID

channel boundaries of the data stream as shown in

Figure 8.

receiving the composite transmit and receive signal

from the line. The line code used in the DNIC is

Biphase and is shown in Figure 10. The scrambled

NRZ data is differentially encoded meaning the

previous differential encoded output is XOR’d with

the current data bit which produces the current

output.

This

is

then

biphase

encoded

where

transitions occur midway through the bit cell with a

negative going transition indicating a logic "0" and a

positive going transition indicating a logic "1".

There are some major reasons for using a biphase

line code. The power density is concentrated in a

spectral

region

that

minimizes

dispersion

and

differential attenuation. This can shorten the line

response and reduce the intersymbol interference

which are critical for adaptive echo cancellation.

There are regular zero crossings halfway through

every bit cell or baud which allows simple clock

extraction at the receiving end. There is no D.C.

content in the code so that phantom power feed may

be applied to the line and simple transformer

coupling may be used with no effect on the data. It is

bipolar, making data reception simple and providing

a high signal to noise ratio. The signal is then passed

through a bandpass filter which conditions the signal

for the line by limiting the spectral content from

The resulting transmit signal will have a distributed

high or by writing DLO (bit 6) of the Diagnostics

to allow this pin to be left not connected in

applications where this function is not required. The

receive

signal

is

the

above

transmit

signal

superimposed on the signal from the remote end and

any reflections or delayed symbols of the near end

signal.

The frame format of the transmit data on the line is

shown in Figures 11 and 12 for the DN mode at 80

and 160 kbit/s. At 80 kbit/s a SYNC bit for frame

recovery, one bit of the D-channel and the B1-

channel are transmitted. At 160 kbit/s a SYNC bit,

the HK bit, two bits of the D-channel and both B1 and

B2 channels are transmitted.

If the DINB bit of the Control Register is set, the

entire D-channel is transmitted during the B1-

channel timeslot. In MOD mode the SYNC, HK and

D-channel bits are not transmitted or received but

rather a continuous data stream at 80 or 160 kbit/s is

present. No frame recovery information is present on

the line in MOD mode.