Warning. Atmel AT91SAM9263-EK

Section 6

Warning

6.1

BMS Signal Sampling

The following behavior and its consequences are related to an AT91SAM9263 device issue described in the Errata section of the AT91SAM9263 datasheet (“BMS: BMS does not have correct state”). The text below is a reminder of this issue and a Workaround proposal at the board level.

Description

The BMS signal, which is multiplexed with the PB3/AC97RX PIO needs to be sampled at a High Level for the AT91SAM9263 microcontroller to boot out of the internal ROM.

At power up, the on-board AC97 device negates its “SDATA_IN” output pin and due to this fact, the

BMS_PB3/AC97RX pin needs to be isolated during the reset phase.

The MN20 gate, controlled by the NRST signal, achieves this, but with the default ERSTL value in the reset controller (refer to the RSTC section in the AT91SAM9263 datasheet for more details), when the

VDDBU power supply is applied for more than 1.2 seconds before the VDDCORE power supply, the

AT91SAM9263 microcontroller samples the BMS signal one Slow Clock (SLCK) cycle after the NRST signal rising (See

Figure 6-1 ).

As a result, the BMS signal is sampled at a Low Level and the AT91SAM9263 boots out of the external

EBI device connected to NCS0.

AT91SAM9263-EK Evaluation Board User Guide 6-1

6325D–ATARM–26-Aug-09

Warning

Figure 6-1. BMS Signal Sampling

SLCK

MCK

Backup Supply

(VDDBU)

POR output backup_nreset processor_nreset

NRST

(nrst_out)

Startup Time

Processor Startup

= 3 cycles

Any

Freq.

EXTERNAL RESET LENGTH

= 2 cycles

BMS_PB3/AC97RX

BMS signal sampling

Workaround:

A t th e fir s t V D D B U p o w e r up o r i f t h i s p o w e r s u p p l y h a s be e n s h u t d o w n ( J 4 - 1 op e n e d

(VDDBU/VDDBACKUP Jumper) or the CR1225 battery cell (J3) removed or changed), the following power-up sequence has to be applied in order to boot out of the internal ROM:

1.

Close J2 to force power on

2.

Open J5 (Boot Mode Select Jumper)

3.

Power on the board

4.

Remove and replace J4-1 (VDDBU/VDDBACKUP Jumper)

6-2

6325D–ATARM–26-Aug-09

AT91SAM9263-EK Evaluation Board User Guide