i.MX RT1180 EtherCAT Interface Design Explained
1. Overview
This article describes the signal functions and connection recommendations for the i.MX RT1180 EtherCAT interface, covering PHY selection, clock and reset signals, MII/RMII interfaces, synchronization and latch signals, and status indication signals. It serves as a reference for EtherCAT hardware design.
2. PHY Selection
The i.MX RT1180 EtherCAT controller uses Beckhoff IP. PHY selection must comply with the requirements in Beckhoff's PHY Selection Guide, available at the following link: https://download.beckhoff.com/download/document/io/ethercat-development-products/an_phy_selection_guidev3.2.pdf
The i.MX RT1180 EtherCAT controller supports MII/RMII interfaces. Therefore, select a PHY that supports the corresponding interface; do not use a PHY that supports only RGMII.
3. EtherCAT Interface Signals and Connection Recommendations
ECAT Signal
Description and Recommendations
CLKOUT25M
Configuring the pin for the CLKOUT25M function enables a 25 MHz clock output. This clock shares the same source as ECAT_CLK_ROOT and requires no additional register configuration for clock division. It is strongly recommended to connect this signal to the XTAL inputs of both PHYs for better clock synchronization. If this signal is not used, an external 25 MHz clock source must be provided for the PHYs.
RESET_OUT
This signal must be connected to the reset inputs of both PHYs. If PHY reset is controlled only through a GPIO, the PHYs cannot be reset through the EtherCAT protocol. RESET_OUT is active high. If the PHY reset input is active low, additional inverting logic is required.
SCL, SDA
Connect to an external EEPROM.
MDC,MDIO
PHY management interface used to access the registers of a PHY based on its address. In i.MX RT1180 EtherCAT applications, the hardware addresses of the two PHYs must be consecutive.
(MII/RMII Interface)
MII (Recommended)
RMII
PT0_RX_CLK/PT1_RX_CLK
Connect to the RX_CLK pin of PHY0/PHY1
Refer to the selected PHY's datasheet: if REF_CLK is provided through its RX_CLK pin, connect to that pin and leave TX_CLK unconnected.
PT0_RX_DV/PT1_RX_DV
Connect to the RX_DV pin of PHY0/PHY1
PT0_RX_ER/PT1_RX_ER
Connect to the RX_ER pin of PHY0/PHY1
PT0_RXD_0/PT1_RXD_0
Connect to the RXD_0 pin of PHY0/PHY1
PT0_RXD_1/PT1_RXD_1
Connect to the RXD_1 pin of PHY0/PHY1
PT0_RXD_2/PT1_RXD_2
Connect to the RXD_2 pin of PHY0/PHY1
Leave unconnected
PT0_RXD_3/PT1_RXD_3
Connect to the RXD_3 pin of PHY0/PHY1
Leave unconnected
PT0_TX_CLK/PT1_TX_CLK
Connect to the TX_CLK pin of PHY0/PHY1
Refer to the selected PHY's datasheet: if REF_CLK is provided through its TX_CLK pin, connect to that pin and leave RX_CLK unconnected.
PT0_TX_EN/PT1_TX_EN
Connect to the TX_EN pin of PHY0/PHY1
PT0_TXD_0/PT1_TXD_0
Connect to the TXD_0 pin of PHY0/PHY1
PT0_TXD_1/PT1_TXD_1
Connect to the TXD_1 pin of PHY0/PHY1
PT0_TXD_2/PT1_TXD_2
Connect to the TXD_2 pin of PHY0/PHY1
Leave unconnected
PT0_TXD_3/PT1_TXD_3
Connect to the TXD_3 pin of PHY0/PHY1
Leave unconnected
LINK_MII_0/LINK_MII_1
Connect to the Link Status outputs of PHY0/PHY1, respectively. Refer to the selected PHY's datasheet for the specific pins. These signals must be connected; otherwise, EtherCAT will not function properly.
SYNC_OUT_0/SYNC_OUT_1
Two hardware synchronization output signals generated by the EtherCAT Distributed Clocks, corresponding to SYNC0 and SYNC1, respectively. Whether to route these signals out depends on the application requirements.
LATCH_IN_0/LATCH_IN_1
External event input signals used to latch the current Distributed Clock System Time when an event occurs. These signals may be left unconnected if not used.
LED_ERR,LED_RUN,LED_STATE_RUN
EtherCAT status indication LED signals.
LINK_ACT_0/LINK_ACT_1
Indicate the link and activity status of the EtherCAT slave. Connect to the Link/Activity LEDs for Port 0/Port 1, respectively.
It is important to distinguish between the following two types of signals: LINK_MII_0/LINK_MII_1: Link Status signals from the PHYs that reflect the link status. These are input signals to the EtherCAT controller. LINK_ACT_0/LINK_ACT_1: Link and activity status signals output by the EtherCAT controller to drive the Link/Activity LEDs. The link and activity status LEDs can be controlled by either the ESC or the PHY, at the designer's discretion.
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