Hardware Description

Table 3-25 JTAG related signals (continued)

Name

Description

Function

RTCK

Return TCK

 

(to JTAG equipment)

Some devices sample TCK and delay the time at which a component actually captures data. Using a mechanism called adaptive clocking, the RTCK signal is returned by the core to the JTAG equipment, and the TCK is not advanced until the core has captured the data. In adaptive clocking mode, RealView ICE or Multi-ICE waits for an edge on RTCK before changing TCK. In a multiple device JTAG chain, the RTCK output from a component connects to the TCK input of the next device in the chain.

nCFGEN

Configuration enable

nCFGEN is an active LOW signal used to put the boards into

 

 

configuration mode. In configuration mode all FPGAs and PLDs

 

 

are connected to the scan chain so that they can be configured by the

 

 

JTAG equipment. (The TAP controller in the PB926EJ-S is not

 

 

accessible.)

 

 

 

nSRST

System reset

nSRST is an active LOW open-collector signal that can be driven

 

(bidirectional)

by the JTAG equipment to reset the target board. Some JTAG

 

 

equipment senses this line to determine when a board has been reset

 

 

by the user.

 

 

This is also used in configuration mode to control the initialization

 

 

pin (nINIT) on the FPGAs.

 

 

Though not a JTAG signal, nSRST is described because it can be

 

 

controlled by JTAG equipment.

 

 

 

nTRST

Test reset (from JTAG

This active LOW open-collector signal is used to reset the JTAG

 

equipment)

port and the associated debug circuitry on the ARM926EJ-S PXP

 

 

Development Chip. It is asserted at power-up, and can be driven by

 

 

the JTAG equipment. This signal is also used in configuration mode

 

 

to control the programming pin, nPROG, on FPGAs.

 

 

 

DBGRQ

Debug request

DBGRQ is a request for the processor core to enter the debug state.

 

(from JTAG equipment)

It is provided for compatibility with third-party JTAG equipment.

 

 

 

ARM DUI 0224I

Copyright © 2003-2010 ARM Limited. All rights reserved.

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ARM ARM DUI 0224I manual Jtag related signals Name Description Function, Rtck, Return TCK, Ncfgen, Dbgrq