XRT7250 datasheet(277/463 Pages) EXAR

277 / 463 page

XRT7250

áç

DS3/E3 FRAMER IC

REV. 1.1.1

258

In Figure 114 the Terminal Equipment samples the

TxOHFrame signal being "High" at rising clock edge #

0. From this point, the Terminal Equipment will wait

until it has detected the 10th rising edge of the TxO-

HClk signal. At this point, the Terminal Equipment

knows that the XRT7250 is just about to process the

“A” bit within a given outbound E3 frame. Additionally,

according to Table 49, the 10th overhead bit to be

processed is the "A" bit. In order to facilitate the

transmission of the Yellow Alarm, the Terminal Equip-

ment must set this "A" bit to "1". Hence, the Terminal

Equipment starts this process by implementing the

following steps concurrently.

a. Assert the TxOHIns input pin by setting it "High".

b. Set the TxOH input pin to "1".

After the Terminal Equipment has applied these sig-

nals, the XRT7250 will sample the data on both the

TxOHIns and TxOH signals upon the very next falling

edge of TxOHClk (designated as "10-" in Figure 114).

Once the XRT7250 has sampled this data, it will then

insert a "1" into the "A" bit position, in the outbound

E3 frame.

Upon detection of the very next rising edge of the Tx-

OHClk clock signal (designated as clock edge 1 in

Figure 114, the Terminal Equipment will negate the

TxOHIns signal (e.g., toggles it "Low") and will cease

inserting data into the Transmit Overhead Data Input

Interface.

After the Terminal Equipment has performed this in-

sertion procedure, it leaves the remaining overhead

bits (within this particular outbound E3 frame) in-tact,

by terminating this Overhead Bit Insertion proce-

dure. The Terminal Equipment should now terminate

this overhead bit insertion, by doing the following.

a. Assert the TxOHIns input pin by setting it "High".

b. Set the TxOH input to "0".

If the Terminal Equipment wishes to continue its

transmission of the Yellow Alarm condition to the Re-

mote Terminal Equipment, then it should resume the

Overhead Bit Insertion procedure (as described

above), at the beginning of each outbound E3 frame

(or each time TxOHFrame is sampled "High”).

5.2.2.2

Method 2 - Using the TxInClk and TxO-

HEnable Signals

Method 1 requires the use of an additional clock sig-

nal, TxOHClk. However, there may be a situation in

which the user does not wish to add this extra clock

signal to their design, in order to use the Transmit

Overhead Data Input Interface. Hence, Method 2 is

FIGURE 114. ILLUSTRATION OF THE SIGNAL THAT MUST OCCUR BETWEEN THE TERMINAL EQUIPMENT AND THE

XRT7250 IN ORDER TO CONFIGURE THE XRT7250 TO TRANSMIT A YELLOW ALARM TO THE REMOTE TERMINAL

EQUIPMENT

Terminal Equipment/XRT7250 Interface Signals

TxOHClk

TxOHIns

TxOHFrame

TxOH

Remaining Overhead Bits with E3 Frame

A bit = 1

TxOHFrame is sampled “high”

Terminal Equipment asserts TxOHIns and

Data on TxOH line.

10 10-

XRT7250 Framer device samples TxOH and

TxOHIns signals

XRT7250 Datasheet(PDF) 277 Page - Exar Corporation

XRT7250 Datasheet(HTML) 277 Page - Exar Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL