CN8330
2.0 Functional Description
DS3/E3 Framer with 52 Mbps HDLC Controller
2.3 Transmitter Operation
The PPDL transmitter can be used with a nibble-wide interface for DS3
SMDS applications if desired. To enable nibble-wide transmission, both the
Nibble Mode Enable [Nibble;CR05.0] and DisPPDL bits in the PPDL Control
Register should be set to one. Data should be inserted on the TDAT[3:0] pins;
MSB on TDAT[2], second MSB on TDAT[1], next MSB on TDAT[0], LSB on
TDAT[3] in response to TXBCK/TXGAPCK (which now occurs every 4 bits). In
nibble mode, the nibbles are transmitted MSB first and are nibble-aligned after
each overhead bit in the DS3 frame for a total of 21 nibbles per 85-bit data block.
Nibble mode should not be used for E3 applications. In this mode (Nibble mode
and PPDLONLY pin = 0), the transmit PPDL interface shifts the serial data by
one bit. This anomaly (only on the transmit side) can be remedied by the circuit
shown in Figure 2-9.
Figure 2-9. Nibble Mode with the PPDLONLY Control Pin Low
CN8330
TDAT[3]
Nibble Data
Register
TDAT[2]
TDAT[1]
TDAT[0]
Q3
Q2
Data Bit
Input Pin
Q1
Q0
MSB
2SB
1SB
LSB
Q Output
TDAT[2]
TDAT[1]
TDAT[0]
D Input
TDAT[3]
D
Q
CK
TXBCK
CK
D-Type FF
•
100441E
Conexant
2-19
CONEXANT [ CONEXANT SYSTEMS, INC ]
