AM263P4-Q1: Safety error pin

Hi Whitney,

Apologies for the late response here.

Whitney Ballard said:

So do we  configure (program )  this pin to be an Output OR an Input?   If not,  how does it function as both an output and an input?  

SAFETY_ERRORn pin would only act as output pin, whose output is driven by an ESM. There's no additional configuration needed to configure this pin as output. As mentioned in the section "ESM Error Pin Output" in TRM (AM263Px Sitara Microcontrollers Technical Reference Manual (Rev. C), following is the reason why an Input buffer is present: "The I/O input from the cell should be looped back to the err_i input. In this way, the status of the error I/O can be directly observed from the I/O buffer loopback path (using the register "ESM_PIN_STS Register"), instead of just from the internal state to the ESM."

Whitney Ballard said:

Why  would it need a pull down resister if the signal is actively driven as an output of the AM263P4?  Does the signal need a pull down resister to make sure the input buffer reads it as a logic low? 

The SAFETY_ERRORn signal is implemented on an LVCMOS voltage buffer pin and can be configured to operate as open-drain output. This has been done by configuring the ESM module to source a constant low output and toggle the output enable. The output buffer drives low when enabled and is high impedance when disabled. I've filed an internal bug to add this to the AM263P datasheet. 

Please also refer to the AM263P CC or EVM schematics to see the implementation.

Regards,

Sahana

You have stated that the SAFETY_ERRORn pin would only act  as an output pin, whose output is driven by an  ESM.   But the data sheet  indicates it is an IO  (Input and an Output).  From the AM263P data sheet.  Table 5 - 107,  system Signal Descriptions:      

The "IO" indicates Input and an output.    So when you say it is only an output,  I am confused.   Is the data sheet wrong? 

Also,  in the Data sheet,  Table 5.4  ,  Pin Connectivity Requirements,  it says  :    

This  raises a few questions.   It says that  this pin must be connected to ground through a  pull down resister if  a Printed wiring board signal trace is connected to it and it is not actively driven by an attached ( I assume external to the AM263P processor)  device.  But if we put a pull down resister and it is configured to be open drain output as you mentioned above,  it would never go high.  You would need a pull UP resister to 3.3Volts to have it go high.    Can the output be configured (programmed)  to be open drain OR an active driver?  

Also if it is an output only,  why would we be driving it with an active device?  

I did  look in the Technical Reference Manual,  13.6.3.4.3,  ESM Error Pin Output,   and it had some info,  especially this paragraph. 

It says that during Power on reset,  the error pin is asserted low by the SoC which drives it with a weak pull down resister AND that the customer may also add an external pull down resister that is ONLY active during POR.     Is this the pull down resister they are referring to in the Pin Connectivity Requirements above?  So I should put an external pull down resister in,  but only have it active  during POR?   

Also  concerning your statement above   "The I/O input from the cell should be looped back to the err_i input. In this way, the status of the error I/O can be directly observed from the I/O buffer loopback path (using the register "ESM_PIN_STS Register"), instead of just from the internal state to the ESM."

How is this loop back accomplished?  Is this loop back internal to the SOC?  Is it programmable such that the I/O input is looped back  OR is not looped back? 

It does not appear that the err_i  input   is a separate pin on the AM263P processor. 

Thank you 

Whitney Ballard  

Sahana:  In your response you said:  

"The SAFETY_ERRORn signal is implemented on an LVCMOS voltage buffer pin and can be configured to operate as open-drain output. This has been done by configuring the ESM module to source a constant low output and toggle the output enable. The output buffer drives low when enabled and is high impedance when disabled. I've filed an internal bug to add this to the AM263P datasheet. "

Can the Safety_errorn pin be configured to by either a open drain OR an active driver?   I would assume that  if we program it to be an open drain,   we would have to supply a pull up resister to 3.3 volts to get it to go logic high when it is the high impedance state,  please confirm.   

Thank you 

Whitney Ballard