Article Details

ID: 2009
Case Type: faq
Category: Device Modeling
Related To: IBIS
Family: MachXO

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Which IBIS models should I use for the MachXO JTAG signal pins?

For the JTAG input pins, use the LVCMOS input models, input threshold
voltage is referenced using the VCCAUX value, and select the model that has:

  • TCK: bus keeper = NONE
  • TDI: bus keeper = pull up
  • TMS: bus keeper = pull up

For the JTAG output pin TDO, use LVCMOS output type, with fast slew setting and
pull up on. Set the output current setting as follows:

  • VCCJ=3.3v, use 8ma current setting
  • VCCJ=2.5v, use 8ma current setting
  • VCCJ=1.8v, use 8ma current setting
  • VCCJ=1.5v, use 8ma current setting
  • VCCJ=1.2v, use 6ma current setting

The VCCJ value for output drive is discussed on page 8-4 of the "MachXO sysIO Usage Guide" TN1091.

where it states:

"The VCCIO of one of the banks is also used to power the JTAG pins (Bank1 for
MachXO256, Bank2 for MachXO640 and Bank5 for MachXO1200 and MachXO2280 devices).
Therefore, the threshold of the JTAG pins is determined by the VCCIO of the
JTAG bank."

This statement can be clarified by examining Table 8.2 in TN1091. The output
standard will follow the bank Vccio. The input standard will accommodate both
LVCMOS2.5 and LVCMOS3.3, regardless of Vccio, as the input thresholds are
references to Vccaux.

The IBIS models for MachXO devices are available at: