User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 10: Serial Interfaces Page
343
The example in
has the sync pulse set at time 0. The map table will be reset to entry 0 after the
configured delay and then determine when DOUT is driven. In the example the delay is one (sync is sampled
on the clock edge) and the data is driven for at least the first four bit times.
Figure 71: Example Transmission Using TIN as Active High Sync (transition/sampling on rising clock
edge)
S
YNCHRONOUS
S
ERIAL
P
ROTOCOL
E
NGINE
The protocol engine converts between the bit streams used by the line interface and the packets transferred
by the DMA engines. It has two modes, configured in the
ser_mode
register. In HDLC mode frames are
encoded on the bit stream using the HDLC protocol. In transparent mode the bit stream is packed into bytes
and the framing is based on the line interface Enable signal.
O
PERATION
IN
HDLC M
ODE
In the HDLC mode the frame structure used by the DMA engines is converted into the HDLC form on the line.
The protocol engine can perform the following functions:
•
insertion and deletion of HDLC flags
•
bit stuffing and de-stuffing
•
CRC calculation and checking
•
address filtering (optional)
•
frame length checking - padding of short frames to a configured minimum frame size (optional)
shows the HDLC frame structure (lengths in bytes).
Clock
Time:
TIN/Sync
DOUT
0
1
2
3
Table 226: HDLC Frame Structure
Flag (U) (01111110)
Address (1 to 2)
Control/Data (1 to MAX)
CRC (2 or 4)
Flag/Abort (1) (01111110) or
(01111111)
Bit Stuffed