NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

Signal Terminations for the Silicon Explorer

From: Silicon Explorer II User's Guide (11/01)

Note that the SX-S devices are derived from SX-A die.

• The probing of an SXA device requires special setup because it requires a 70 ohm termination on all the probe connectors (TDI, TDO, TCK, TMS, PRA, PRB). The 70 ohm series termination is used to prevent data transmission corruption during probing.
• TRST is an active low input. During JTAG mode and Silicon Explorer debugging mode, JTAG state machine's reset must not be active, otherwise probe circuitry is disabled. Below is the recommendation for TRST pin in JTAG and Silicon Explorer:
  • RTSX Rev0 - No TRST pin
  • RTSX Rev1 - You must tie TRST pin high when doing JTAG and Silicon Explorer
  • RTSX Rev2 - You can leave the TRST pin floating (or drive it high - it must not be driven low) when running JTAG or Silicon Explorer if "Reserve JTAG TRST" was selected in Designer.
  • SXA - You can leave the TRST pin floating when running JTAG or Silicon Explorer

Sample Silicon Explorer Terminations for an RT54SX72S/CQ256
Note: The circuit above is in dedicated JTAG mode so no pull-up resistor is needed on TMS.

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Last Revised: November 01, 2003
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