DS3141 datasheet(61/88 Pages) DALLAS

61 / 88 page

DS3141/DS3142/DS3143/DS3144 Single/Dual/Triple/Quad DS3/E3 Framers

61 of 88

RHDLC1

Receive HDLC FIFO Data

5Ch

Bit #

Name

Default

—

Note: After the RHDLC2 register is read, the receive FIFO read pointer advances and both the RHDLC1 and RHDLC2 registers are updated

with the next data/status from the receive FIFO. The host processor should read RHDLC1 first to retrieve the FIFO data and then immediately

read RHDLC2 to retrieve the associated FIFO status bits.

Bits 0 to 7: Receive FIFO Data (D[7:0]). These bits contain the next byte of receive FIFO data. D0 is the LSB and

is the first bit received by the framer, while D7 is the MSB and is the last bit received. Reading this register does

not cause the receive FIFO read pointer to advance.

RHDLC2

Receive HDLC FIFO Status

5Dh

Bit #

Name

N/A

PS1

PS0

CBYTE

OBYTE

Default

—

Bit 0: Opening Byte Indicator (OBYTE). This bit is set to 1 when the RHDLC1 register contains the first byte of an

HDLC packet.

Bit 1: Closing Byte Indicator (CBYTE). This bit is set to 1 when the RHDLC1 register contains the last byte of an

HDLC packet, whether the packet is valid or not. The host processor can check the PS[1:0] bits to determine

packet validity.

Bits 2, 3: Packet Status (PS[1:0]). These bits are only valid when the CBYTE bit is set to 1. These bits indicate

the validity of the incoming packet and the cause of the problem if the packet was received in error.

PS[1:0]

PACKET STATUS

REASON FOR INVALID RECEPTION OF THE PACKET

Valid

—

Invalid

Corrupt CRC

Invalid

Incoming packet was either too short (less than 4 bytes including the CRC)

or did not contain an integral number of octets

Invalid

Abort sequence detected

Packets fewer than four bytes long (including the FCS) are invalid and the data that appears in the FIFO in such

instances is meaningless. If only one byte is received between flags, then both the CBYTE and OBYTE bits are

set. If two bytes are received, then OBYTE is set for the first byte received and CBYTE is set for the second byte

received. If three bytes are received, then OBYTE is set for the first byte received and CBYTE is set for the third

byte received. In all of these cases, the packet status is reported as PS[1:0] = 10, and the data in the FIFO should

be ignored.

DS3141 Datasheet(PDF) 61 Page - Dallas Semiconductor

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