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Modeling

For trace bit rates of 0-600Mbps, basic signal integrity can be established using simplified modeling. Most of the transmission line model consists of the cable that is used to connect the DSTREAM-ST unit to the target.

  • The 30cm CoreSight cable is made using 0.635mm pitch ribbon, and can be modeled as a 66Ω transmission line, with a 1.5ns propagation delay, and 0.4Ω DC resistance. The connectors at either end of the cable can be modeled as a 0.5pF capacitance to ground.

  • The 15cm CoreSight cable is made using 0.635mm pitch ribbon, and can be modeled as a 66Ω transmission line, with a 0.75ns propagation delay, and 0.2Ω DC resistance. The connectors at either end of the cable can be modeled as a 0.5pF capacitance to ground.

  • The JTAG 20 cable is made using 1.27mm pitch ribbon, and can be modeled as a 100Ω transmission line, with a 1.5ns propagation delay, and 0.1Ω DC resistance. The connectors at either end can be modeled as a 1.0pF capacitance to ground.

  • The MIPI-60 cable is made using 0.5mm pitch micro-coaxial ribbon, and can be modeled as a 50Ω transmission line, with a 1.5ns propagation delay, and 0.1Ω DC resistance. The connectors at either end can be modeled as a 0.25pF capacitance to ground.

The circuit at the DSTREAM-ST end of the transmission line can be modeled using the following primitives:

  • All resistors can be modeled as their ideal resistance values with minimum or zero parasitics.

  • All capacitors can be modeled as their ideal capacitance values with minimum or zero parasitics.

  • Input comparators can be modeled using the Spartan 3 SSTLx_I model. The switching threshold can be assumed to be half of the VTREF voltage, as supplied by the target. The data is valid when it is 100mV above or below this threshold.

  • Output drivers can be modeled using the Spartan 3 LVCMOS Fast 16mA model. You must choose the model voltage to match the target system voltage.

All other parasitics and traces within the DSTREAM-ST are negligible for most purposes.

Note

To achieve good signal integrity, Arm recommends using series termination resistors on all target outputs.

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