Rainbow Electronics DS3131 - Manual (Page 60)

DS3131
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Table 7-B. Receive Bit-Synchronous HDLC Packet Processing Outcomes
OUTCOME CRITERIA
EOF/Normal Packet Integral number of packets > min and < max is received and CRC is okay
EOF/Bad FCS Integral number of packets > min and < max is received and CRC is bad
Abort Detected Seven or more 1s in a row detected
EOF/Too Few Bytes Less than the packet minimum is received (if detection enabled)
Too Many Bytes Greater than the packet maximum is received (if detection enabled)
EOF/Bad Number of Bits Not an integral number of bytes received
FIFO Overflow Tried to write a byte into an already full FIFO
Note: EOF = End of Frame, which means that this outcome is not determined until a closing flag is detected.
If any of the 40 receive HDLC channels detects an abort sequence, a FCS checksum error, or if the
packet length was incorrect, then the appropriate status bit in the status register for DMA (SDMA) is set.
If enabled, the setting of any of these statuses can cause a hardware interrupt to occur. See Section
5.3.2
for details about the operation of these status bits.
Table 7-C. Receive Bit-Synchronous HDLC Functions
Zero Destuff This operation is disabled if the channel is set to transparent mode.
Flag Detection and Byte
Alignment Okay to have two packets separated by only one flag or by two flags sharing 0. This
operation is disabled if the channel is set to transparent mode.
Octet Length Check
The maximum check is programmable up to 65,536 Bytes through the RHPL
register. The maximum check can be disabled through the ROLD control bit in the
RHCR register. The minimum and maximum counts include the FCS. An error is
also reported if a noninteger number of octets occur between flags.
CRC Check
Can be either set to CRC-16 or CRC-32 or none. The CRC can be passed through to
the PCI bus or not. The CRC check is disabled if the channel is set to transparent
mode.
Abort Detection Checks for seven or more 1s in a row.
Invert Data
All data (including the flags and FCS) is inverted before HDLC processing. Also
available in the transparent mode.
Bit Flip
The first bit received becomes either the LSB (normal mode) or the MSB (telecom
mode) of the byte stored in the FIFO. Also available in the transparent mode.
Transparent Mode
If enabled, flag detection, zero destuffing, abort detection, length checking, and
FCS checking are disabled. Data is passed to the PCI bus on octet (byte) boundaries
in unchannelized operation.