ITP700 Debug Port Design Guide

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ITP700 Debug Port Design Guide
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13 Appendix D – Arbitration of the
Scan Chain With a Local TAP
Master
The basic handshaking mechanism is predicated on the notion that when an alternate local TAP
master has requested access to the target system, the debug tool will behave as though it has been
unplugged. This suggests that when control is regained, the debug tool must regain the state
information needed to operate properly.
The protocol is as follows:
1. The ITP de-asserts the DBA# signal when the current task is complete. The ITP however
maintains control of the target system.
2. The local TAP master seeing DBA de-asserted activates an open drain control gate on the ITP
PWR pin, thereby pulling PWR low at the ITP.
3. The ITP isolates all signals connected to the target system.
4. The local TAP master is free to perform any actions with the scan chain it requires. When
finished the local TAP master must release PWR to allow the debug port to regain control of
the scan chain.
5. The ITP seeing PWR asserted, assesses the RESET# state, BCLK(p,n) state, and then re-
configures the target to properly use the BPM[5:0]# signals as indicated.
6. The ITP asserts DBA# to regain control of the target and reset the TAP agents prior to
performing the next task.