UPD360 datasheet(119/221 Pages) MICROCHIP

119 / 221 page

 2016-2017 Microchip Technology Inc.

DS00002084C-page 119

UPD360

11.2.1.1

RX FIFO Write Interface

Figure 11-1 shows how the write interface (from receive hardware's perspective) appears at various points of reception.

Each RX Packet is comprised of two bytes of control information and the received packet data. The Status byte indicates

whether the data is valid and the SOP type that was received. A value of 0x00 in the status byte implies that the data is

not valid (including the NBytes field).When bit 0 of the status byte is 1'b1, the Nbytes field indicates the length of the

packet and bits 6:4 of the status byte indicates the SOP type that was received. An empty FIFO always returns a value

of 0x00. However, the status byte should not be polled, but rather the RX_FIFO_NOT_EMPTY bit in the RX Interrupt

Status Register (RX_IRQ_STAT) should be used. The valid bit is retained for legacy compatibility. When software reads

the packet data from the FIFO, it should only read number of bytes indicated by Nbytes (in addition to the Nbytes and

Status entries). Note that the byte count indicated by NBytes includes the CRC32 data.

When SMBus mode is enabled (via the EN_SMBUS_MODE bit in the RX Control Register A (RX_CTL_A)), the Status

and Nbytes fields are swapped and Nbytes is incremented by 1 to include the status byte. The swapping makes the

(not-recommended) polling of the Status byte impossible for this mode. When software reads the packet data from the

FIFO, it should only read number of bytes indicated by NBytes (in addition to the Nbytes entry). Figure 11-2 details the

format while in SMBus mode.

FIGURE 11-1:

WRITE INTERFACE VIEW OF RX FIFO

FIGURE 11-2:

RX FIFO SMBUS MODE

CRC (4)

byte m

byte 0

Message

Header

CRC (4)

byte n

byte 0

Message

Header

Ram Address

Nbytes*

Status*

CRC (4)

byte n

byte 0

Message

Header

1900h

197Fh

<- Write Head Pointer

*assuming SMBus mode = 0

Free Space

<- Write Head Pointer Plus One

at SOP

Ram Address

Nbytes*

Status*

CRC (4)

byte n

byte 0

Message

Header

1900h

197Fh

Free Space

<- Write Head Pointer Plus One

during packet

reception

<- Write Current Pointer

Ram Address

Nbytes*

Status*

1900h

197Fh

<- Write Head Pointer, Write Current Pointer

Free Space

<- Write Head Pointer Plus One

after packet reception

<- Write Head Pointer

<- Write Current Pointer

byte 0

Message

Header

Reserved for

Nbytes and Status

Reserved for

Nbytes and Status

Nbytes*

Status*

CRC (4)

byte m

byte 0

Message

Header

CRC (4)

byte n

byte 0

Message

Header

SMBus mode = 1

Ram Address

Nbytes*

Status*

1900h

197Fh

<- Write Head Pointer, Write Current Pointer

Free Space

<- Write Head Pointer Plus One

after packet reception

Nbytes*

Status*

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