UPD360 datasheet(120/221 Pages) MICROCHIP

120 / 221 page

UPD360

DS00002084C-page 120

 2016-2017 Microchip Technology Inc.

The packet status and NBytes format are shown in Table 11-2 and Table 11-3, respectively.

When the device detects valid start-of-packet (SOP) signaling, the current write pointer is set to the write head pointer

plus 2. As packet data is received, it is written into the FIFO at the current write pointer and following each write the

current write pointer is incremented. The current write pointer points to the next location to be written. Upon reaching

the top of the RAM, the current write pointer wraps to 0. The byte count is maintained by the RX control block.

When a valid EOP is received and a good CRC residue is indicated by CRC logic, hardware will write the status (valid

bit and received SOP type) to the location addressed by the write head pointer and the number of received bytes to the

location addressed by the write head pointer plus one. SMBus mode will swap the data (and increment the number of

bytes). Following the writing of the status and length, the write head pointer is updated to the current write pointer and

the write head pointer plus one is updated to the current write pointer plus 1 (accounting for the wrap at the top of the

RAM).

If a valid EOP is not received and the bus becomes idle, then an abnormal termination is detected. In this case, the

packet is dropped, i.e., the device will not update the NBytes location or the Status location.

If a valid EOP is detected but the CRC generator indicates an invalid CRC, then the packet is corrupted. The device will

drop the packet and not update the NBytes location or the Status location.

If a more data is received than will fit in the FIFO, then an overrun is detected. The excess data does not get written into

the FIFO and the current write pointer is not incremented.

A separate test is made at the start of the packet to determine if there is sufficient room for the status and length bytes.

In the event of a “no room for header” condition, an overrun is detected. The excess data does not get written into the

FIFO and the current write pointer is not initialized.

If a packet has reached the maximum size allowed (as specified by the RX Maximum Packet Size Register (RX_MAX-

_SIZE)) and more data is received, then an oversize is detected. The excess data does not get written into the FIFO

and the current write pointer is not incremented.

TABLE 11-2:

RXQ STATUS FIELD

Bits

Description

Type

RESERVED

Always reads 0.

6:4

RX_SOP_TYPE

This field indicates the SOP type that was received.

000b: SOP

001b: SOP'

010b: SOP''

011b: SOP'_Debug

100b: SOP''_Debug

101b - 111b: Reserved

3:1

RESERVED

Status

Status of queue data

0b: Data is invalid

1b: Data is valid

TABLE 11-3:

RXQ NUMBER OF BYTES (NBYTES) FIELD

Bits

Description

Type

NBYTES

If EN_SMBUS_MODE is 0, this field represents the number of bytes of valid data in the

packet.

If EN_SMBUS_MODE is 1, this field represents the number of bytes of valid data in the

packet plus 1.

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