Abstract: The DS80C400 datasheet mentions that the DS80C400 RSTOL output should not be connected to the network PHY's reset input. This application note describes the reason for this restriction and shows how the PHY reset input should be used. Overview The DS80C400 data sheet mentions that the DS80C400 RSTOL output should not be connected to the network PHY's reset input. This application note describes the reason for this restriction, and shows how the PHY reset input should be used. Requirements This application note assumes the use of a DS80C400 rev. B1 networked microcontroller and an Intel LXT972A Ethernet PHY. Similar considerations apply to other manufacturers' PHYs, but pinout and pin names may differ. This application note does not apply to the DS80C410 or DS80C411. Background The DS80C400 rev. B1 will not receive network packets when there is no clock signal on the receive clock pin (RXCLK) during reset (other than power-up). When the DS80C400 reset output (RSTOL) and the PHY reset input (RESET) are connected, the DS80C400 puts the PHY into reset—and the PHY is unable to generate the receive clock signal. Solution The solution is to not connect the DS80C400 RSTOL and the PHY's reset input RESET as documented in the DS80C400 data sheet. Configuration Pin Sampling Additional testing has shown that some LXT972A PHYs do not always sample the state of the configuration pins correctly (LED/CFG1, LED/CFG2 and LED/CFG3). This can result in 10Mb operation even though 100Mb were requested, or nonfunctioning LEDs. A 1uF capacitor between the PHY's reset input (RESET) and ground solves this problem. Suggested Circuit The highlighted part of the schematic (Figure 1) shows the proper PHY reset connection. Figure 1. DS80C400 and PHY reset. TINIS400 Socket The TINIs400 socket has been modified to sever the connection between RESET and RSTOL. Figure 2 shows the modification. (TINIs400 ships with this modification applied at the factory.) Figure 2. TINIs400 modification. References Please refer to the High-Speed Microcontroller User's Guide: Network Microcontroller Supplement and the DS80C400/DS80C410/DS80C411 data sheets for more details about the networked microcontrollers. A user discussion board is available. Related Parts   APP 3399: Dec 21, 2004 DS80C400 Network Microcontroller Full Data Sheet (PDF, 1.8MB) Free Samples Automatic Updates Would you like to be automatically notified when new application notes are published in your areas of interest? Sign up for EE-Mail™. We Want Your Feedback!   Download, PDF Format (105kB)  AN3399, AN 3399, APP3399, Appnote3399, Appnote 3399