PM7346 datasheet(98/419 Pages) PMC

98 / 419 page

PM7346 S/UNI-QJET

DATASHEET

PMC-960835

ISSUE 6

SATURN QUAD USER NETWORK INTERFACE FOR J2, E3, T3

PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA INC., AND ITS CUSTOMERS’ INTERNAL USE 77

appended, followed by flags. If the TDPR transmit data FIFO underflows, an

abort sequence is automatically transmitted.

When enabled, the TDPR continuously transmits flags (01111110) until data is

ready to be transmitted. Data bytes to be transmitted are written into the TDPR

Transmit Data Register. The TDPR automatically begins transmission of data

once at least one complete packet is written into its FIFO. All complete packets

of data will be transmitted if no error condition occurs. After the last data byte of

a packet, the CRC FCS (if CRC insertion has been enabled) and a flag, or just a

flag (if CRC insertion has not been enabled) is transmitted. The TDPR then

returns to the transmission of flag characters until the next packet is available for

transmission. The TDPR will also force transmission of the FIFO data once the

FIFO depth has surpassed the programmable upper limit threshold.

Transmission commences regardless of whether or not a packet has been

completely written into the FIFO. The user must be careful to avoid overfilling the

FIFO. Underruns can only occur if the packet length is greater than the

programmed upper limit threshold because, in such a case, transmission will

begin before a complete packet is stored in the FIFO.

An interrupt can be generated once the FIFO depth has fallen below a user

configured lower threshold as an indicator for the user to write more data.

Interrupts can also be generated if the FIFO underflows while transmitting a

packet, when the FIFO is full, or if the FIFO is overrun.

If there are more than five consecutive ones in the raw transmit data or in the

CRC data, a zero is stuffed into the serial data output. This prevents the

unintentional transmission of flag or abort sequences.

Abort sequences (01111111 sequence where the 0 is transmitted first) can be

continuously transmitted at any time by setting a control bit. During packet

transmission, an underrun situation can occur if data is not written to the TDPR

Transmit Data register before the previous byte has been depleted. In this case,

an abort sequence is transmitted, and the controlling processor is notified via the

UDR register bit. An abort sequence will also be transmitted if the user overflows

the FIFO with a packet of length greater than 128 bytes. Overflows where other

complete packets are still stored in the FIFO will not generate an abort. Only the

packet which caused the overflow is corrupted and an interrupt is generated to

the user via the OVR register bit. The other packets remain unaffected.

When the TDPR is disabled, a logical 1 (Idle) is inserted in the path maintenance

data link.

PM7346 Datasheet(PDF) 98 Page - PMC-Sierra, Inc

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