CX28394/28395/28398
3.0 Registers
Quad/x16/Octal—T1/E1/J1 Framers
3.15 Data Link Registers
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 first reading the receiver data link status
[RDL1_STAT; addr 0A9]. In some cases, multiple consecutive status bytes may be placed in the FIFO, so the
processor must always read RDL1_STAT before reading RDL1 to distinguish between WORD0 and WORD1
byte values. However, each time a non-zero byte count [RDL1_CNT] status is read, the processor is guaranteed
the next RDL1_CNT reads from RDL1 will equal message data [WORD1] and not message status. Note that a
status byte occupies 1 byte of FIFO space, just the same as a message data byte occupies 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. Note that 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
zero to indicate that all received data from that message was discarded. Note that 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. Abort
status is reported if the receiver detects a string of 7 or more consecutive ones during an HDLC
message. FCS error status is reported if FCS mode is enabled, and the checksum calculated
over the received HDLC message does not match the received 16-bit FCS. Non-integer error
status is reported if the receiver detects a closing FLAG character that yields an HDLC
message length which is not an integer number of 8-bit octets.
00 = Good
01 = FCS/Non-integer
10 = Abort
11 = Partial
RDL1_CNT[5:0]
Byte Count [5:0]—Indicates the number of Message Data [WORD1] bytes that are stored in
subsequent consecutive FIFO locations, constituting one received message. The reported byte
count is the actual number of bytes, in the range of 0 to 63 bytes, where 0 indicates zero bytes
for the processor to read. The processor can either read the specified number of message data
bytes consecutively from RDL1 or can poll RDL1_STAT after reading each data byte until
RDL1_STAT reports an end of message (i.e. RMPTY1=1 or RSTAT1=1).
100054E
Conexant
3-79
CONEXANT [ CONEXANT SYSTEMS, INC ]
