
XRT79L71
PRELIMINARY
113
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
If the XRT79L71 is operating in C-bit Parity Frame Format then the FEAC bit-field of the DS3 Frame can be
used to transmit FEAC messages (See Figure 49).
The FEAC code word is a 6-bit value which is
encapsulated by 10 framing bits, forming a 16-bit FEAC message of the form:
where [d5, d4, d3, d2, d1, d0] is the FEAC 6-bit code word. The rightmost bit (e.g., a "1") of the FEAC
Message, is transmitted first. Since each DS3 frame contains only 1 FEAC bit, 16 DS3 frame periods are
required to transmit the 16 bit FEAC Code Message.
The following section describes how to use the Transmit FEAC Controller block to transmit a given FEAC
Message.
Operating the Transmit FEAC Controller
In order to transmit a FEAC message to the remote terminal, the user must execute the following steps.
STEP 1 - Write the outbound 6-bit FEAC Code-word into the Transmit DS3 FEAC Register
In this step, the user must write the six bit FEAC code word into the Transmit DS3 FEAC Register. The bit
format of this register is presented below.
FIGURE 48. ILLUSTRATION OF THE FUNCTIONAL BLOCK DIAGRAM OF THE TRANSMIT DIRECTION CIRCUITRY, WHEN-
EVER THE
XRT79L91 DEVICE HAS BEEN CONFIGURED TO OPERATE IN THE DS3 CLEAR-CHANNEL FRAMER MODE
(WITH THE TRANSMIT FEAC CONTROLLER BLOCK HIGHLIGHTED)
FIGURE 49. THE BIT-FORMAT OF A FEAC MESSAGE
0
d5
d4
d3
d2
d1
d0
0
1
Transmit
Payload Data
Input
Interface
Block
Transmit
Payload Data
Input
Interface
Block
Transmit
DS3/E3
Framer
Block
Transmit
DS3/E3
Framer
Block
Tranmit
DS3/E3
LIU Block
Tranmit
DS3/E3
LIU Block
TxSer
TxNib[3:0]
TxInClk
TRING
TTIP
Transmit
Overhead Data
Input Interface
Block
Transmit
Overhead Data
Input Interface
Block
TxOHClk
TxOHIns
TxOHInd
TxOH
TxOHEnable
TxOHFrame
TxNibClk
TxFrame
Tx LAPD
Controller
Block
Tx LAPD
Controller
Block
From Microprocessor
Interface Block
Tx LAPD
Buffer
(90 Bytes)
Tx LAPD
Buffer
(90 Bytes)
Tx FEAC
Processor
Block
Tx FEAC
Processor
Block