How to enable the remote system reset from JTAG

AN3321

2/8

Doc ID 18275 Rev 1

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How to enable the remote system reset from JTAG

The EVALSPEAr310 board (EVB) has a standard "Multi-ICE JTAG Interface" connector,

named J26. Through J26, it is possible to connect a JTAG adapter (refer to Appendix F of

the reference document [1.]). The connector supports separate reset signals for JTAG-TAP

(nTRST pin) and for the board system (nSRST pin).

On the EVB rev 2.0, the actual circuit for system reset is not able to receive a remote reset

from the JTAG connector. This can affect the debugging activity, forcing the developer to

reset manually by pressing the on-board reset button.

Note:

1

All the modifications listed below are mandatory.

2

A basic skill on soldering tools is required.

Here below you can find the list of all the modifications required on the EVB to enable

remote system reset through JTAG.

Before starting, you need the following components:

●

one device P/N STM6315SDW13F

●

one resistor in package 0603, value 0 ohm. It can be replaced with a short wire

connection.

Connecting the nSRST pin of the JTAG connector

The EVB default assembly configuration has one resistor (R329) missing, isolating nSRST

pin. To connect nSRST pin:

●

Mount the R329 resistor, 0 ohm. It is located close to the JTAG connector on the

bottom layer.

Joining all reset signals in a single wire

On the revision 2.0 of the board, the reset is distributed through the unidirectional device

U12. By design, U12 blocks nSRST signals to go from JTAG to system reset, and prevents

JTAG to reset all on-board components. To connect the nSRST signal to the system reset,

modify the top layer of the board as follows (see Figure 1: EVB top layer):

1.

Remove U12, located near the JTAG connector.

2.

Solder together pins 7, 8 and 9 of U12.

3.

Solder together pins 11, 12, 13, 14, 15, 16, 17 and 18 of U12.

Figure 3 shows the area of U12 after these modifications.

This is an ESD sensitive device, improper handling can cause permanent damage to

the on-board components.