AN3321

How to enable the remote system reset from JTAG

Doc ID 18275 Rev 1

3/8

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