AM335x SYSBOOT pins

Hiroyasu Tazawa1

Guru 12350 points

Hi, Everyone

I have a question about SYSBOOT pin of AM335x

SYSBOOT and other function are multiplex.
My customer want to use rts/cts of UART below:

U1 pin　uart2_ctsn Pull-up
U2 pin uart2_rtsn Pull-up

U3 pin　uart3_ctsn Pull-down
U4 pin uart3_rtsn Pull-down

V2 pin　uart3_ctsn Pull-down
V3 pin uart3_rtsn Pull-down

Actually I think my customer should eveluate their system.

but I guess TI think this situation.
Are these connection O.K ?
Do these connection have any probrems ?

Best Regards
Hiroyasu

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

These functions are not pinmuxed on the pins shown. I don't understand the question.

0 Hiroyasu Tazawa1 over 9 years ago in reply to Biser Gatchev-XID

Guru 12350 points

Hi, Biser

Thank you for your response.

My customer use ZCZ package device.

For example Datasheet mrntion about U1 pin

(5) annotation says below

User should fix Pull-up and Pull-down for SYSBOOT pin when boot.
but after boot My customer want to use this pin as other function.
(in this case, They want uart2_ctsn after boot)

Best Regards
Hiroyasu

http

://e2e.ti.com/support/arm/sitara_arm/f/791/p/558858/2045642#2045642

0 Biser Gatchev-XID over 9 years ago in reply to Hiroyasu Tazawa1

TI__Guru**** 393215 points

Do they want to use the internal pullup/pulldown resistors?

0 Stanislav Stilyanov over 9 years ago in reply to Hiroyasu Tazawa1

TI__Mastermind 23440 points

Hi Hiroyasu,
Main point is to not allow CTS pins to be driven by the external UART device during POR. This will interfere with the pullups/pulldowns which set the SYSBOOT pins during POR.
This is valid for any other SYSBOOT pin used as input later by application.

0 Hiroyasu Tazawa1 over 9 years ago in reply to Biser Gatchev-XID

Guru 12350 points

Hi, Biser

Thank you for your reply.
I think User can not use internal pullup/pulldown.
Because SYSBOOT pin is latch during POR.
User have to set pullup/pulldown by external hardware.

Best Regards
Hiroyasu

0 Hiroyasu Tazawa1 over 9 years ago in reply to Stanislav Stilyanov

Guru 12350 points

Hi Stanislav

Thank you for your reply.

After booting, User can change pinmux by software. but hardware is not changed.
Normally, I think the UART interface does not pull up / pulldown.
but AM335x have to set SYSBOOT pin using external hardware.

Can user use UART interface after booting in this case ?

===========
U1 pin　uart2_ctsn Pull-up
U2 pin uart2_rtsn Pull-up

U3 pin　uart3_ctsn Pull-down
U4 pin uart3_rtsn Pull-down

V2 pin　uart3_ctsn Pull-down
V3 pin uart3_rtsn Pull-down
===========

Best Regards
Hiroyasu

0 Biser Gatchev-XID over 9 years ago in reply to Hiroyasu Tazawa1

TI__Guru**** 393215 points

I know that external pulls must be used for SYSBOOT settings. What I meant is whether they want to use the internal pulls for operating mode settings. If this is the case the external pulls should be calculated in such a way, that they do not override internal pulls when they are switched on after reset.

Further, what Stanislav has warned you is that if you have external device outputs connected to the SYSBOOT lines, you must take precautions that these outputs do not drive the line opposite to the required SYSBOOT level at reset release time.

0 Hiroyasu Tazawa1 over 9 years ago in reply to Biser Gatchev-XID

Guru 12350 points

Hi, Biser

Thank you.
I got it !

Best Regards
hiroyasu

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AM335x SYSBOOT pins