Bt8370/8375/8376
2.0 Circuit Description
2.8 Transmitter
Fully Integrated T1/E1 Framer and Line Interface
Fs and MFAS errors are controlled by the TMERR bit in the TERROR
register. TMERR commands a single Fs bit error in T1, or MFAS bit error in E1
by logically inverting the next multiframe bit transmitted.
CAS Multiframe (MAS) errors are controlled by the TSERR bit in the
TERROR register. TSERR commands a single MAS pattern error by logically
inverting the first MAS bit transmitted.
2.8.7 In-Band Loopback Code Generator
The in-band loopback code generator circuitry overwrites the transmit data with
in-band codes of configurable value and length. These codes are sequences with
periods of 1 to 7 bits and may, in some applications, overwrite the framing bit.
The Transmit Inband Loopback Code Configuration register [TLB; addr 077]
controls the functions required for this operation.
A loopback code is generated in the transmit data stream by writing the
loopback code to the Transmit Inband Loopback Code Pattern register [LBP; addr
078], and then by setting the Start Inband Loopback (LBSTART) and Loopback
Length (LB_LEN) bits in the Transmit Inband Loopback Code Configuration
register [TLB; addr 077]. The TLB register optionally allows the loopback code
to overwrite framing bits using the UNFRAMED bit. The LB_LEN provides
loopback code pattern lengths of 4 to 7 bits. Patterns of 2 or 3 bits can be achieved
by repeating the pattern in 4- or 6-bit modes, respectively. Framed or unframed all
1s or all 0s can also be achieved by setting the pattern to all 0s or all 1s. The
in-band loopback code generator is applicable only to T1 mode.
2.8.8 ZCS Encoder
The ZCS encoder encodes the single rail clock and data (unipolar) into dual rail
data (bipolar). The Transmit Zero Code Suppression Bits (TZCS[1,0]) in the
Transmitter Configuration register [TCR1; addr 071] selects ZCS and Pulse
Density Violation (PDV) enforcement options for XTIP/XRING and
TPOSO/TNEGO output pins. TZCS supports the following: Alternate Mark
Inversion (AMI), High Density Bipolar of order 3 (HDB3), Bipolar with 8 Zero
Suppression (B8ZS), Pulse Density Violation (PDV), Unassigned Mux Code
(UMC), and Bipolar with 7 Zero Suppression (B7ZS).
NOTE: ZCS encoding, which alters data content, is performed prior to the CRC
calculation so the outgoing CRC will always be correct.
The AMI line code requires at least 12.5% average 1s density and no more
than 15 consecutive 0s. A 1 is encoded as either a positive or negative pulse; a 0 is
the absence of a pulse. Two consecutive pulses of the same polarity are referred to
as a Bipolar Violation (BPV).
N8370DSE
Conexant
2-65
CONEXANT [ CONEXANT SYSTEMS, INC ]
