ETRAX 100LX HW Design Notes

SDRAM clock during reset

  • The SDRAM needs the clock during ETRAX 100LX reset cycle to prevent the system from boot failure in case the reset occurs during an SDRAM read cycle. See the ETRAX 100LX Errata and the MCM4+16 schematics, page 3, for more details.
    Note The MUX workaround is already implemented in the ETRAX 100LX MCM 4+16.

Network boot

  • The Ethernet MDIO-signal needs a pull up resistor to make the network boot reliable. The pull up resistor is needed even if the MDIO-signaling isn't used.
    Note The pull up resistor is already mounted in the ETRAX 100LX MCM 4+16.

Ethernet PHY clock during reset

  • The Ethernet PHY needs the clock signal during it's reset but the ETRAX 100LX does not drive the clock signal during the reset. The AXIS' standard solution is extending the reset signal, to the Ethernet PHY, by using double reset circuits. See the the ETRAX 100LX design example, pages 1 and 3, for an example.
    Note The double reset circuits are already implemented in the ETRAX 100LX MCM 4+16.


  • The clock signal must come from a jitter-free oscillator.
  • External PLL-based oscillators does usually not work very well.
  • Oscillators generating “clock spread” doesn't work at all.

Wait input signal

  • The WAIT-signal needs a pull up resistor. If it is left unconnected (floating) it can cause all sorts of strange intermittent problems. See the ETRAX 100LX Designer's Reference, section “5.10 Wait Input and Bus Cycle Rerun”, for details.
    Note The pull up resistor is already mounted in the ETRAX 100LX MCM 4+16.

Boot select signals

  • The boot select (bs) signals are actively driven as outputs a short while after reset and must not be hardwired high or low. Use pull up and/or pull down resistors to configure the wanted boot mode. For more information see sections “6 BOOTSTRAP METHODS” and “19.5 Logic Analyzer Mode and Test Signals” in the ETRAX 100LX Designer's Reference.

Migrating from the 100LX MCM to the 100LX

  • If you want to replace the ETRAX 100LX MCM with an ETRAX 100LX and external memories in your design you can find some useful notes here: Migrating from 100LX MCM to 100LX

axis/hw_design_notes.txt · Last modified: 2008/04/29 16:19 by jesper
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