40- and 100-Gbps Ethernet MAC and PHY MegaCore Function User Guide

ID 683114
Date 6/15/2022
Public
Document Table of Contents

3.4.2.3. 2‑Wire Serial Interface Registers

Several optical modules use the 2‑wire serial interface protocol, which requires only limited resources. This interface uses two, bidirectional open‑drain lines, a serial data line (SDA) and a serial clock (SCL). The master node drives the clock and addresses slaves. Data is sent most significant bit first. The slave node receives the clock and address. Unlike the MDIO protocol, the 2-wire serial interface can include multiple masters. In addition, the master and slave roles may be changed after a STOP message is sent. The interface has an eight‑bit address space, so a maximum of 255 nodes can communicate. The interface runs at 400 KHz.

Table 69.  2‑Wire Serial Interface Registers Describes the 2‑wire serial registers in the 40-100GbE IP core example design. Refer to the datasheet for your 2‑wire device for more information.
Note: The 2‑wire serial interface in the IP core example design does not support the specialized CRC-8 check or multibyte transaction modes.

Address

Name

Bits

Description

HW Reset Value

Access

0x420

2WS_WDATA

[7:0]

Data to be written.

0x00

RW

0x421

2WS_RDATA

[31]

When asserted, the link is busy.

1b’0

R

[30]

When asserted, indicates that the slave failed to acknowledge during the previous operation.

1b’0

R

[7:0]

Result of previous read.

0x00

R

0x422

2WS_ADDR

[15:8]

Slave address.

0xA0

RW

[7:0]

Memory address.

0x00

RW

0x423

2WS_CMD

[1]

When asserted, indicates a write command.

0x0

RW

[0]

When asserted, indicates a read.

0x0

RW