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XRT79L71
PRELIMINARY
469
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
NOTE: The shaded rows designate those Overhead bits that the XRT79L71 can be inserted into the outbound E3 data-
stream via the Transmit Overhead Data Input Interface block. The un-shaded rows designate those Overhead bits
that the XRT79L71 CANNOT insert into the outbound E3 data-stream.
TASK # 3: After the System-Side Terminal Equipment has waited the appropriate number of TxOHEnable
pulses from the TxOHFrame signal being sampled "High", it should assert the TxOHIns input signal by pulling
it "High". Concurrently, the System-Side Terminal Equipment should also place the appropriate value of the
overhead bit to be inserted into the outbound E3 data-stream onto the TxOH input signal. The Transmit
Overhead Data Input Interface block will sample and latch the data residing on the TxOH input pin upon the
second rising edge of TxInClk after TxOHEnable was sampled "High".
TASK # 4: The System-Side Terminal Equipment should hold the TxOHIns input pin "High" and also hold the
value of the TxOH signal stable until the next time the TxOHEnable outout pin is sampled "High". Afterwards,
the System-Side Terminal Equipment should toggle the TxOHIns input pin "Low" and wait until another
appropriate TxOHEnable pulsing period comes up, for inserting an overhead bit into the outbound E3 data-
stream.
CASE STUDY: The System-Side Terminal Equipment intends to insert the appropriate overhead bits
into the Transmit Overhead Data Input Interface using Method 2 in order to transmit the FERF/RDI
indicator to the remote terminal equipment.
For E3, ITU-T G.832 applications, the FERF/RDI indication is transmitted by setting the FERF/RDI bit-field (Bit
1 within the MA-byte, of each outbound E3 frame) to "1".
If we were to assume that the connection between the System-Side Terminal Equipment and the Transmit
Overhead Data Input Interface block of the XRT79L71 is as illustrated in Figure 223, then Figure 224 presents
an illustration of the signaling that must go on between the System-Side Terminal Equipment and the Transmit
Overhead Data Input Interface when using Method 2.
53
GC Byte, Bit 6
YES
54
GC Byte, Bit 7
YES
55
GC Byte, Bit 8 (LSB)
YES
TABLE 61: THE RELATIONSHIP BETWEEN THE NUMBER OF PULSES IN THE TXOHENABLE SIGNAL, SINCE THE
TXOHFRAME SIGNAL WAS LAST SAMPLED "HIGH" TO THE E3 OVERHEAD BIT THAT IS CURRENTLY BEING PROCESSED
BY THE
TRANSMIT OVERHEAD DATA INPUT INTERFACE BLOCK
NUMBER OF PULSES IN TXOHENABLE,
SINCE
TXOHFRAME BEING SAMPLED
"HIGH"
THE OVERHEAD BIT TO BE PROCESSED
BY THE
TRANSMIT OVERHEAD DATA INPUT
INTERFACE BLOCK
CAN THIS OVERHEAD BIT BE ACCEPTED
BY THE
XRT79L71, AND INSERTED INTO
THE OUTBOUND
E3 DATA-STREAM?