Maxim DS33Z41 specifications Transmit Packet Processor

DS33Z41 Quad IMUX Ethernet Mapper

8.16 Transmit Packet Processor

The Transmit Packet Processor accepts data from the Transmit FIFO performs bit reordering, FCS processing, packet error insertion, stuffing, packet abort sequence insertion, inter-frame padding, and packet scrambling. The data output from the Transmit Packet Processor to the Transmit Serial Interface is a serial data stream (bit synchronous mode). HDLC processing can be disabled (clear channel enable). Disabling HDLC processing disables FCS processing, packet error insertion, stuffing, packet abort sequence insertion, and inter-frame padding. Only bit reordering and packet scrambling are not disabled.

Bit reordering changes the bit order of each byte. If bit reordering is disabled, the outgoing 8-bit data stream DT[1:8] with DT[1] being the MSB and DT[8] being the LSB is output from the Transmit FIFO with the MSB in TFD[7] (or 15, 23, or 31) and the LSB in TFD[0] (or 8, 16, or 24) of the transmit FIFO data TFD[7:0] 15:8, 23:16, or 31:24). If bit reordering is enabled, the outgoing 8-bit data stream DT[1:8] is output from the Transmit FIFO with the MSB in TFD[0] and the LSB in TFD[7] of the transmit FIFO data TFD[7:0]. In bit synchronous mode, DT [1] is the first bit transmitted.

FCS processing calculates an FCS and appends it to the packet. FCS calculation is a CRC-16 or CRC-32 calculation over the entire packet. The polynomial used for FCS-16 is x16 + x12 + x5 + 1. The polynomial used for FCS-32 is x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x + 1. The FCS is inverted after calculation. The FCS type is programmable. If FCS append is enabled, the calculated FCS is appended to the packet. If FCS append is disabled, the packet is transmitted without an FCS. The FCS append mode is programmable. If packet processing is disabled, FCS processing is not performed.

Packet error insertion inserts errors into the FCS bytes. A single FCS bit is corrupted in each errored packet. The FCS bit corrupted is changed from errored packet to errored packet. Error insertion can be controlled by a register or by the manual error insertion input (LI.TMEI.TMEI). The error insertion initiation type (register or input) is programmable. If a register controls error insertion, the number and frequency of the errors are programmable. If FCS append is disabled, packet error insertion will not be performed. If packet processing is disabled, packet error insertion is not performed.

Stuffing inserts control data into the packet to prevent packet data from mimicking flags. A packet start indication is received, and stuffing is performed until, a packet end indication is received. Bit stuffing consists of inserting a zero directly following any five contiguous ones. If packet processing is disabled, stuffing is not performed.

There is at least one flag plus a programmable number of additional flags between packets. The inter-frame fill can be flags or all ones followed by a start flag. If the inter-frame fill is all ones, the number of ones between the end and start flags does not need to be an integer number of bytes, however, there must be at least 15 consecutive ones between the end and start flags. The inter-frame padding type is programmable. If packet processing is disabled, inter-frame padding is not performed.

Packet abort insertion inserts a packet abort sequences as necessary. If a packet abort indication is detected, a packet abort sequence is inserted and inter-frame padding is done until a packet start flag is detected. The abort sequence is FFh. If packet processing is disabled, packet abort insertion is not performed.

The packet scrambler is a x43 + 1 scrambler that scrambles the entire packet data stream. The packet scrambler runs continuously, and is never reset. In bit synchronous mode, scrambling is performed one bit at a time. In byte synchronous mode, scrambling is performed 8 bits at a time. Packet scrambling is programmable.

Once all packet processing has been completed serial data stream is passed on to the Transmit Serial Interface.

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