BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
346
Section 10: Serial Interfaces
Document
1250_1125-UM100CB-R
The transmitter can be temporarily paused (for example as the result of a flow control request) by writing the
tx_pause bit in the
ser_cmd
register. This causes the transmitter to complete sending the current packet and
then suspend operation until re-enabled. The next packet will wait in the TxFIFO while the transmitter is
paused. The tx_pause_complete flag in the
ser_status
register will be set to acknowledge completion of a
tx_pause command. The flag is set immediately if there is no packet in flight when the command is issued,
otherwise it will be set when the end of the current packet is moved from the TxFIFO into the transmit module.
When the transmit module is idle, either Flag (octet synchronous) or Idle (bit synchronous) can be sent onto
the channel as configured by flag_en in the
ser_mode
register.
HDLC Receiver
In HDLC mode, frames within the bit stream are self-identifying. The Protocol Engine monitors the input bit
stream supplied by the line interface. Frame recognition begins with a Flag not followed by another Flag, an
Abort or an Idle.
The receive module first removes any bit stuffing to extract the bytes of the frames delimited by the opening
and closing flags.
The first step in processing is frame filtering based on the HDLC address. The bit mask in the ser_addr_mask
configuration register selects address bits from within the first two bytes following the opening Flag of each
frame. A frame is accepted if its masked address bits match any of the four address registers, ser_usr0_addr
through ser_usr3_addr, under the same mask. Otherwise the frame is rejected and not sent to the RxFIFO.
shows the address matching logic.
Figure 72: Frame Address Matching
Mask
2nd Byte 1st Byte
USR0_ADDR
15
0
15
0
8 7
15
0
Match
Match_USR0
Match_USR1
Match_USR2
Match_USR3