XRT7250 Datasheet, PDF (174/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

áç
DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
FIGURE 58. 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
TxOHFrame
TxOHIns
TxOH
0 0- 1
2
3
4
5
6
7
8 8-
X bit = 0
Remaining Overhead Bits with DS3 Frame
X bit = 0
TxOHFrame is sample “high”
Terminal Equipment asserts
“TxOHIns” and data on “TxOH” line
XRT7250 device samples the TxOHIns and
TxOH signals.
TxOHFrame is sample “high”
Terminal Equipment asserts
“TxOHIns” and data on “TxOH” line
XRT7250 device samples the TxOHIns and
TxOH signals.
In Figure 58 the Terminal Equipment samples the Tx-
OHFrame signal being "High" at the rising clock edge
# 0. At this point, the Terminal Equipment knows that
the XRT7250 is just about to process the very first
overhead bit within a given outbound DS3 frame. Ad-
ditionally, according to Table 21, the very first over-
head bit to be processed is the first X bit. In order to
facilitate the transmission of the Yellow Alarm, the
Terminal Equipment must set this X bit to 0. Hence,
the Terminal Equipment starts this process by imple-
menting the following steps concurrently.
a. Assert the TxOHIns input pin by setting it "High".
b. Set the TxOH input pin to 0.
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 at 0- in Figure 58.
Once the XRT7250 has sampled this data, it will then
insert a "0" into the first X bit position, in the outbound
DS3 frame.
Upon detection of the very next rising edge of the Tx-
OHClk clock signal (designated as clock edge 1 in
Figure 58), 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, until rising clock edge # 8 (of the TxOHClk
signal). According to Table 21, rising clock edge # 8
indicates that the XRT7250 is just about ready to pro-
cess the second X bit within the outbound DS3 frame.
Once again, in order to facilitate the transmission of
the Yellow Alarm this X-Bit must also be set to 0.
Hence, the Terminal Equipment will (once again) im-
plement the following steps, concurrently.
a. Assert the TxOHIns input pin by setting it "High".
155