PROCESSOR-SDK-AM335X: Unused pins termination

Eby Jayan

HI,
We are using Am335X processor for our System On chip module (SOM). We have taken out interfaces as UART,SPI ,USB,CAN,I2C and remaining as GPIOs.

This SOM will be plugged into base cards with the required external interfaces fro application

If i,m not using any of these interfaces in my base board , what is the recommended method for termination of the unused signals / ports from hardware prospective

can I leave it as floating without any interference threats . Or should I implement any pull up/ down externally

Regards

Eby

over 8 years ago

0 Yordan Kovachev over 8 years ago

TI__Guru**** 161600 points

This is explained in the schematic checklist:
processors.wiki.ti.com/.../AM335x_Schematic_Checklist

Best Regards,
Yordan

0 Eby Jayan over 8 years ago in reply to Yordan Kovachev

Expert 2115 points

HI Yordan
Thanks for your reply , The not gives an idea of the pins which are not used at all .
What if a pin is configured as UART in software and not used in the hardware - in such cases what should be done ? same with SPI and I2C

Ie all the UARTs , SPI, I2C are available at the interface connector of MY SOM and all are enabled in software , but these are not used in the base board . In such cases what should be done .
can i leave open ?

Regards
Eby

0 Biser Gatchev-XID over 8 years ago in reply to Eby Jayan

TI__Guru**** 393215 points

Unused pins should not be enabled in software. You should think of some way that software can distinguish what base board is attached and configure peripherals accordingly. On TI EVM boards an ID EEPROM is used for this purpose. Software reads the board ID from it and configures the processor accordingly.

0 Eby Jayan over 8 years ago in reply to Biser Gatchev-XID

Expert 2115 points

HI Biser,
We are selling this as a SOM to customers with all the UARTs , I2C and SPI enabled . the use the interfaces depends on the customers application.
So what should we advice to them to consider for the unused pins provided the software does not change

Regards
Eby

0 Biser Gatchev-XID over 8 years ago in reply to Eby Jayan

TI__Guru**** 393215 points

They should leave the unused outputs floating, and the unused inputs tied to the inactive level.

0 Eby Jayan over 8 years ago in reply to Biser Gatchev-XID

Expert 2115 points

HI Biser ,
Inactive level in the sense Pull up/ pull down ?

0 Biser Gatchev-XID over 8 years ago in reply to Eby Jayan

TI__Guru**** 393215 points

Yes.

0 Eby Jayan over 8 years ago in reply to Biser Gatchev-XID

Expert 2115 points

Thanks Biser,
One more doubt .
what will be the default state of the GPIOs will it be in input mode or in output mode .

Regards
Eby

0 Biser Gatchev-XID over 8 years ago in reply to Eby Jayan

TI__Guru**** 393215 points

See Table 4-1 in the AM335x Datasheet Rev. J.

0 Eby Jayan over 8 years ago in reply to Biser Gatchev-XID

Expert 2115 points

HI Biser,
When you say "keep the unused inputs tied to the inactive level." does it mean it is in Software or external Pull up/down in hardware.
also able 4-1 in the AM335x Datasheet Rev. J. does not say that the GPIO is in Input mode or Output mode . It says it I/O.
Regards
Eby

0 Biser Gatchev-XID over 8 years ago in reply to Eby Jayan

TI__Guru**** 393215 points

You are looking at "TYPE". Look at "BALL RESET STATE" "BALL RESET RELEASE STATE" and "RESET REL. MODE".

0 Eby Jayan over 8 years ago in reply to Biser Gatchev-XID

Expert 2115 points

Thanks for the clarification on the I/O type .

Please clarify the below query
When you say "keep the unused inputs tied to the inactive level." does it mean it is in Software or external Pull up/down in hardware.

Regards

Eby

0 Biser Gatchev-XID over 8 years ago in reply to Eby Jayan

TI__Guru**** 393215 points

You already posted that you cannot change software, so obviously it has to be done externally.

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PROCESSOR-SDK-AM335X: Unused pins termination