XRT7250 Datasheet, PDF (358/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
Operation of the Transmit Payload Data Input In-
terface
The Transmit Terminal Input Interface is extremely
flexible, in that it permits the user to make the follow-
ing configuration options.
• The Serial or the Nibble-Parallel Interface Mode
• The Loop-Timing or the TxInClk (Local Timing)
Mode
Further, if the XRT7250 has been configured to oper-
ate in the TxInClk mode, then the user has two addi-
tional options.
• The XRT7250 is the Frame Master (e.g., it dictates
when the Terminal Equipment will initiate the trans-
mission of data within a new E3 frame).
• The XRT7250 is the Frame Slave (e.g., the Termi-
nal Equipment will dictate when the XRT7250 ini-
tiates the transmission of a new E3 frame).
Given these three set of options, the Transmit Termi-
nal Input Interface can be configured to operate in
one of the six (6) following modes.
• Mode 1 - Serial/Loop-Timed Mode
• Mode 2 - Serial/Local-Timed/Frame Slave Mode
• Mode 3 - Serial/Local-Timed/Frame Master Mode
• Mode 4 - Nibble/Loop-Timed Mode
• Mode 5 - Nibble/Local-Timed/Frame Slave Mode
• Mode 6 - Nibble/Local-Timed/Frame Master Mode
Each of these modes are described, in detail, below.
6.2.1.1 Mode 1 - The Serial/Loop-Timing Mode
The Behavior of the XRT7250
If the XRT7250 has been configured to operate in this
mode, then the XRT7250 will behave as follows.
A. Loop-Timing (Uses the RxLineClk signal as the
Timing Reference)
Since the XRT7250 is configured to operate in the
loop-timed mode, the Transmit Section (of the
XRT7250) will use the RxLineClk input clock signal
(e.g., the Recovered Clock signal, from the LIU) as its
timing source. When the XRT7250 is operating in this
mode it will do the following.
1. It will ignore any signal at the TxInClk input pin.
2. The XRT7250 will output a 34.368MHz clock sig-
nal via the RxOutClk output pin. This clock signal
functions as the Transmit Payload Data Input
Interface block clock signal.
3. The XRT7250 will use the rising edge of the
RxOutClk signal to latch in the data residing on
the TxSer input pin.
B. Serial Mode
The XRT7250 will accept the E3 payload data from
the Terminal Equipment, in a serial-manner, via the
TxSer input pin The Transmit Payload Data Input In-
terface will latch this data into its circuitry, on the ris-
ing edge of the RxOutClk output clock signal.
C. Delineation of Outbound E3 frames
The XRT7250 will pulse the TxFrame output pin
"High" for one bit-period, coincident with the
XRT7250 processing the last bit of a given E3 frame.
D. Sampling of Payload Data, from the Terminal
Equipment
In Mode 1, the XRT7250 will sample the data at the
TxSer input, on the rising edge of RxOutClk.
Interfacing the Transmit Payload Data Input Inter-
face block of the XRT7250 to the Terminal Equip-
ment for Mode 1 Operation
Figure 157 presents an illustration of the Transmit
Payload Data Input Interface block (within the
XRT7250) being interfaced to the Terminal Equip-
ment, for Mode 1 operation.
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