STM32H503 - Timing feasibility using an external RTC

[prahaladh_srinath]

Hi...

Greetings...

We're planning to use STM32H503 MCU in our application.

To brief about our application, we've a parallel RTC IC which has gone EOL. This RTC receives commands from the motherboard MCU. So, we're mimicking the RTC's functionality using a microcontroller and a serial RTC in a castellation PCB (smallest form factor). With the microcontroller's GPIO, we're trying to achieve parallel interface. Attached the timing diagram in this thread. Since it's a time critical application, we are preferring to go with a high speed MCU.

The flow of timing diagram goes like this...

When CS0 becomes low, the address is present in the address bus (4 bit). When CS0 goes low, within min. 50ns, Read / Write pin goes low.

During read operation, the data corresponding to the address needs to be placed in data bus (4 bits of data) within 120ns max. During write operation, the data needs to be read from the data bus within 90ns.

Considering the crucial timing, we are checking the feasibility to use STM32H503 MCU (32 pin variant)

Kindly let us know the minimum instruction time of that MCU when it's clocked at Max. 250MHz (internal clock source). As the PCB dimensions are too small, we're expecting the smallest package for the MCU.

Kindly provide your comments on whether our timing requirements before met by STM32H503 MCU. Also kindly confirm if the 32 pin variant in that series support internal RTC.

Best Regards,

Prahaladh S

[SofLit · Accepted solution]

Hello and welcome to the community.

First,

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Attached the timing diagram in this thread.

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You forgot to attach the diagram. Please attach it to let others in the community help you.

Second, and regarding your last question, this information is available in the STM32H503 datasheet / table 2 :

[tiedangdang]

What is the model of the discontinued chip? It is convenient to find a replacement

[prahaladh_srinath]

Hi...

Thank you for your response. Apologies for not attaching the timing diagram in the thread.

Attaching in this thread for further proceedings...

Best Regards,

Prahaladh S

[SofLit]

Ok thank you. But since STM32H503 device features already an RTC, why do you need to connect an external RTC then?

[prahaladh_srinath]

Thank you for your response. 

Yes. Our basic architecture is to use an external RTC to meet our requirement. If the MCU has an internal RTC, we can very well use that.

Thanks & Regards,

Prahaladh S

[SofLit]

But becarefull, with 32 pin package VBAT pin is not available, so you can't back the time up with an external battery. VBAT is tied internally to VDD in that case.

[prahaladh_srinath]

Hi,

Okay. Thank you for the information. For our application, battery backup for RTC isn't required.

Best Regards,

Prahaladh S

[SofLit]

Hello,

In that case could we consider that thread closed? and mark the comment that answered your question "Accept as Solution"?

[prahaladh_srinath]

Hi...

Regarding the internal RTC, we are clear with the response.

We would like to know whether the timing mentioned in the timing diagram be met by the MCU - STM32H503. 

Also, we would like to know what's the minimum instruction time when the clock is 250 MHz (internal source need to be used based on the size constraint).

Best Regards,

Prahaladh S