Bt8370/8375/8376
3.16 Data Link Registers
FFC[5:0]
Fully Integrated T1/E1 Framer and Line Interface
Near Full FIFO Threshold—Selects FIFO depth of near full interrupt [RNEAR; addr 009] and
near full level status [RNEAR1; addr 0A9]. The RNEAR interrupt and RNEAR1 indicator are
both activated when the number of empty FIFO locations equals the selected threshold. The
threshold controls how many data and/or status bytes (64 minus threshold value) that the
processor must read from RDL1 after the RNEAR interrupt so it can clear the RNEAR1
indicator. The threshold also determines how much time remains (in bytes) for the processor to
read RDL1 before the receive FIFO is full. If a receive message is in progress when the near
full threshold is reached, the receiver issues a message interrupt [RMSG; addr 009] and places
a Partial message in the receive FIFO.
FFC[5:0]
00 0000
00 0001
00 0010
|
Empty @ RNEAR
none
Filled @ RNEAR
64 = RFULL
63 filled
1 empty FIFO location
2 empty FIFO locations
|
62 filled
|
11 1110
11 1111
64 empty FIFO locations
63 empty FIFO locations
1 filled
0 filled = empty
0A8—Receive Data Link FIFO #1 (RDL1)
Two different read byte values are supplied: WORD0 equals message status, and WORD1 equals message data.
The processor determines which byte value is located in the FIFO by reading the receiver data link status
[RDL1_STAT; addr 0A9]. In some cases, multiple consecutive status bytes can be placed in the FIFO, so the
processor must always read RDL1_STAT before reading RDL1. This allows it to distinguish between WORD0
and WORD1 byte values. However, each time a non-0 byte count [RDL1_CNT] status is read, the processor is
guaranteed that the next byte read from RDL1 will be message data [WORD1], not message status. Status byte
and a message data byte each occupy 1 byte of FIFO space.
WORD0: Message Status
7
6
5
4
3
2
1
0
EOM[1]
EOM[0]
RDL1_CNT[5]
RDL1_CNT[4]
RDL1_CNT[3]
RDL1_CNT[2]
RDL1_CNT[1]
RDL1_CNT[0]
EOM[1, 0]
End of Message—Receive data link reports an End of Message status for each occurrence of a
complete (Good), a continued (Partial), an errored (FCS/Non-integer), or an aborted (Abort)
message.
Properly received unformatted messages are reported with a Partial end of message status.
The processor responds to Good or Partial status by reading the indicated number of data bytes
[RDL1_CNT] from RDL1. For abort or error cases, RDL1_CNT equals 0 to indicate all that
received data from that message was discarded.
A Good status with RDL1_CNT=0 is reported if the processor reads RDL1 while the
receiver is in progress of filling the FIFO (in which case RDL1_STAT contains RSTAT1=1 and
RMSG1=1). If an abort or error status with zero byte count is reported after the processor has
already buffered a prior HDLC partial message, that partial buffered processor data should be
discarded.
3-96
Conexant
N8370DSE
CONEXANT [ CONEXANT SYSTEMS, INC ]
