AM6412: UART speed

Hello,

Please check the answers below:

Questions on 7.10.5.18 (UART):

1. Does this interface has max. speed of 115200 at 30pF load?

Ans: Please refer Table 7-146. UART Switching Characteristics , 30pF mode

2. What if load is less than 30pF, what is the max. speed interface can run?

Ans: Please refer Table 7-146. UART Switching Characteristics, 15pF mode (this is TBD  for now)

Let me check and confirm

3. 30pF load is for the TX or RX line?

Ans: Please refer Table 7-144 for OUTPUT CONDITIONS

Let me check and confirm

Questions on 7.10.5.16.4 (PRU_ICCSG UART)

1. Specification specs. this interface to run at 12Mbps. Is this correct?

Ans: Please refer table 7-124 PRU_ICSSG UART Switching Characteristics

2. 12Mbps is at what capacitive load?

Regards

Rajashri

Waiting for Q2 and Q3. 

We want to run UART at higher speeds (~3Mbps). Can you suggest if we can run 7.10.5.18 UART at those speeds? 

If yes, what should be the loading capacitance?

Also, in UART signal is sampled 16 times, does TI samples the 8th sample to check if bit is 1 or 0?

Thanks,
Darshan

Hello Darshan, 

Thank you for following up on the queries. 

2. What if load is less than 30pF, what is the max. speed interface can run?

The datasheet has been update recently with the available data. We do not have additional information to share.

3. 30pF load is for the TX or RX line?

Please refer below specs 

We want to run UART at higher speeds (~3Mbps). Can you suggest if we can run 7.10.5.18 UART at those speeds? 

Please refer below 

8.4.2.21 UART
The UART module supports the following main features:
• 16C750 compatibility
• Baud rate from 300 bps up to 3.6864 Mbps (subject to functional clock frequency)
• Auto-baud between 1200 bps and 115.2 Kbps

If yes, what should be the loading capacitance?

Also, in UART signal is sampled 16 times, does TI samples the 8th sample to check if bit is 1 or 0?

I need to check internally on the availability of the data or information that can be shared. Please expect a delay in response as i check internally. 

Regards,

Sreenivasa

Hello Darshan, 

Below is the additional question i received over email

The datasheet mentions that UART can only run at max. speed of 115200 at 30pF load. We are using the uart interface to talk to another card and want to run at max speed (>3Mbps). The uart will be routed a few inches on the control board and then a few inches on the other card. 

We will be above the 30pF loading requirement, but still want to run the UART at 3.4Mbps. What would be the best possible solution for us? 

Should we use a transceiver like SN74AVC4T245 to help drive the signal?

With the question on would an external SN74AVC4T245 help/solve the problem of not meeting the datasheet capacitance value I think that is what is often done or the point of adding one. Transceivers are used in general in cases where distance on PCB or number of connectors is increasing.

Regards,

Sreenivasa

Hi Sreenivas,

Based on 8.4.2.21 snippet you shared above, we can run UART at 3.6864Mbps with 30pF output load and 5V/ns input conditions?

As 30pF load capacitance requirement for TX line, should not this be a requirement for remote device RX? What is the reason why 30pF a requirement for TX output signal?

Also, in UART signal is sampled 16 times, does TI samples the 8th sample to check if bit is 1 or 0?

Can you suggest what is the output load capacitance requirement for SN74AVC4T245?

Hello Darshan, 

Thank you for the inputs. 

Please find reply below 

Also, in UART signal is sampled 16 times, does TI samples the 8th sample to check if bit is 1 or 0?

This is an IP question, i am not sure if this info is available as pubic info and i am checking on this internally. Please expect a delay in reply.

Can you please help me understand the use case for the question and where are you reading that the  UART signal is sampled 16 times ?

As 30pF load capacitance requirement for TX line, should not this be a requirement for remote device RX?

Please refer to the UART timing conditions, TX is output driving the load and RX is the receiver. For the remote RX, the specs would be the slew rate.

What is the reason why 30pF a requirement for TX output signal?

The switching characteristics and timings are specified for a given load. The value you are referring is the datasheet specs and i do not have the internal implementation details to answer the query.

Can you suggest what is the output load capacitance requirement for SN74AVC4T245?

This is customer specific use case. Please refer below inputs provided over email by pekka. 

"Gagan, I was just stating I see transceivers used in general in cases where distance on PCB or number of connectors is increasing. I’m not directly saying this TI transceiver make the capacitance meet the AM64x datasheet values.".

Please start a SN74AVC4T245  specific thread if you would more details.

Regards,

Sreenivasa