A.2. JTAG interface signals

Table A.1 describes the signals on the JTAG interfaces.

Table A.1. JTAG signals

Signal

I/O

Description

DBGACK

-

This pin is connected in the RealView ICE run control unit, but is not supported in the current release of the software. It is reserved for compatibility with other equipment to be used as a debug acknowledge signal from the target system. It is recommended that this signal is pulled LOW on the target.

DBGRQ

-

This pin is connected in the RealView ICE run control unit, but is not supported in the current release of the software. It is reserved for compatibility with other equipment to be used as a debug request signal to the target system. The RealView ICE software maintains this signal as LOW.

When applicable, RealView ICE uses the core's scan chain 2 to put the core in debug state. It is recommended that this signal is pulled LOW on the target.

GND

-

Ground.

nSRST

Input/output

Active Low output from RealView ICE to the target system reset, with a 4.7kΩ pull-up resistor for de-asserted state. This is also an input to RealView ICE so that a reset initiated on the target can be reported to the debugger.

This pin must be pulled HIGH on the target to avoid unintentional resets when there is no connection.

nTRST

Output

Active Low output from RealView ICE to the Reset signal on the target JTAG port, driven to the VTref voltage for de-asserted state. This pin must be pulled HIGH on the target to avoid unintentional resets when there is no connection.

RTCK

Input

Return Test Clock signal from the target JTAG port to RealView ICE. Some targets must synchronize the JTAG inputs to internal clocks. To assist in meeting this requirement, you can use a returned, and retimed, TCK to dynamically control the TCK rate. RealView ICE provides Adaptive Clock Timing, that waits for TCK changes to be echoed correctly before making more changes. Targets that do not have to process TCK can ground this pin.

RTCK is not supported in SWD mode.

TCK

Output

Test Clock signal from RealView ICE to the target JTAG port. It is recommended that this pin is pulled LOW on the target.

TDI

Output

Test Data In signal from RealView ICE to the target JTAG port. It is recommended that this pin is pulled HIGH on the target.

TDO

Input

Test Data Out from the target JTAG port to RealView ICE. It is recommended that this pin is pulled HIGH on the target.

TMS

Output

Test Mode signal from RealView ICE to the target JTAG port. This pin must be pulled HIGH on the target so that the effect of any spurious TCKs when there is no connection is benign.

Vsupply

Input

This pin is not connected in the RealView ICE run control unit. It is reserved for compatibility with other equipment to be used as a power feed from the target system.

VTref

Input

This is the target reference voltage. It indicates that the target has power, and It must be at least 0.628V. VTref is normally fed from Vdd on the target hardware and might have a series resistor (though this is not recommended). There is a 10kΩ pull-down resistor on VTref in RealView ICE.


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