AM335x SYSBOOT pins which are not cared for ROM code

Daisuke Maeda

Guru 20285 points

Can the SYSBOOT pins which are not cared for ROM code be left floating? Or should they be connected to ground?

For example, the SYSBOOT[7:6] pins are used only in EMAC boot. In a boot mode except EMAC, can they be left floating?

Our customer wants to reduce the number of the parts on their boards.

Best regards,

Daisuke

over 11 years ago

0 Biser Gatchev-XID over 11 years ago

TI__Guru**** 393215 points

Hi Daisuke,

It will be better to tie them either to ground or pull them up.

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 20285 points

Hi Biser,

Thank you for your reply.

If the pins are left floating, what adverse effect does it have?

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

Are these pins connected somewhere else on the design?

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 20285 points

Hi Biser,

Thank you for your reply.

These pins are not connected somewhere else on the design. Since our customer wants to reduce the number of the parts on the design, these pins are left floating.

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

These pins are latched in the control_status register on the power-on reset rising edge, so I would recommend tying them to a defined state.

0 Daisuke Maeda over 11 years ago in reply to Biser Gatchev-XID

Guru 20285 points

Hi Biser,

Thank you for your reply.

Since zero is defined state for all SYSBOOT pins, the SYSBOOT pins which are not cared for ROM code will be connected to ground.

Best regards,

Daisuke

0 Biser Gatchev-XID over 11 years ago in reply to Daisuke Maeda

TI__Guru**** 393215 points

This is the right decision.

0 Biser Gatchev-XID over 11 years ago in reply to Biser Gatchev-XID

TI__Guru**** 393215 points

Just make sure these pins are always configured as inputs.

0 peaves over 11 years ago in reply to Biser Gatchev-XID

TI__Guru 63445 points

It is very dangerous connecting pins that can be configured as outputs directly to ground. A software error can accidentally configure any one or more of these pins to output mode driven high which will short the respective VDDSHVx power rail to ground through the device.

Pull-down resistors only cost about $0.01 each. This seems like a small price to pay to guarantee this never happens. The customer needs to decide if the cost is worth the risk because they are responsible for the results of this decision.

Regards,
Paul

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AM335x SYSBOOT pins which are not cared for ROM code