ST AN3321 APPLICATION NOTE

AN3321

Application note

How to enable remote reset from JTAG on

EVALSPEAr310 board rev 2.0

Introduction

This application note provides information on how to modify the evaluation board for
SPEAr310 (EVALSPEAr310) rev 2.0 to enable remote system reset through the JTAG
interface.

Remote reset is a feature not available by default on EVALSPEAr310 board, but it can help
during software debug activity.

November 2010 Doc ID 18275 Rev 1 1/8

www.st.com

How to enable the remote system reset from JTAG AN3321

1 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.

This is an ESD sensitive device, improper handling can cause permanent damage to
the on-board components.

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.

2/8 Doc ID 18275 Rev 1

AN3321 How to enable the remote system reset from JTAG

Creating a "wired AND" reset

To comply with JTAG specifications, the reset wire has to be a "wired AND" of "open drain"
devices with a common pull-up resistor. The actual reset chip U11 does not have any "open
drain" output. To make this feature available:

● Replace the reset chip U11 with a STM6315SDW13F.

U11 is located close to JTAG connector on the bottom layer (see Figure 2: EVB bottom

layer). Passive pull-up is already available (R242).

Cleaning-up reset wire

On the actual revision of the board, some optional delay circuits are installed adding high
load to reset wire. This is not compliant with JTAG specifications. To solve this issue modify
the top layer of the board as follows (see Figure 1: EVB top layer):

1. Remove R137 and C57, located near the SMII PHY U18

2. Remove R172 and C75, located near the SMII PHY U19

3. Remove R207 and C90, located near the SMII PHY U20

4. Remove C236, located near the SMII PHY U21. Be careful NOT to remove R242

Doc ID 18275 Rev 1 3/8