nvSRAM with disabled RTC function

[NaMo_1534561]

Hello,

Customers are considering replacing current parts with new parts.

1) The CY14B116M has an RTC function, but this function will be not used.
The following pins are not wired on the customer's existing board and will be open.
  INT, Xout, Xin, V_RTcap, V_RTbat

I believe it is correct way when RTC function is not used on this device.

2) CY14B116M has an RTC Register.
What will happen as a device if a write operation is performed on this register?
Since there is no status pin, the write transaction seems to have completed normally from the host, and I understand that if I read it, I can read the RTC register. Is this correct?

MPN:
CY14B116N-ZSP45XI: Now in use
CY14B116M-ZSP25XI: Under consideration

Best Regards,

Naoaki Morimoto

[PradiptaB_11 · Accepted solution]

Hi Morimoto-san,

Please find my comments below.

1. When you are not using the RTC functionality in an nvSRAM with RTC, the RTC-related pins of the part (X_IN, X_OUT, V_RTCcap, and V_RTCbat) must be left floating as already you have pointed out.  Also, you must ensure that the RTC oscillator is disabled by setting the OSCEN bit  to ‘1’ and performing a software store after tRTCp. 

2. When not using the RTC feature the last 16 address used for RTC registers do not have any utility. You may write to bits which are writable in the register and later read them but from any application point of view it does not add value to the application. All the register you will read will not have the correct data and when you are disabling the RTC feature it is suggested to leave out the RTC register addresses from any form of manipulation.(R/W)

Thanks,

Pradipta.

[NaMo_1534561]

Hello Pradipta-san,

Thank you for your answer. There is one concern about Q2.

Does OSCEN bit always have to be disabled "1"?

The current board uses another nvSRAM without RTC functionality (CY14B116N) and the host is already using this address.

The OSCEN bit may be irregularly rewritten to 0 or 1 during operation, and there is no guarantee that the register value will be 1.

Best Regards,

Naoaki Morimoto

[PradiptaB_11]

Hi Morimoto-san,

It is better to not read/write to RTC registers if not using the RTC functionality. If in the application irregular read/write happen on the OSCEN bit you might observe an increase in power consumption for some time but this will not affect the normal read/write operations on the memory. So if the application is not power constrained it will impact close to null when you write a 1 on OSCEN bit.

Thanks,

Pradipta.

[NaMo_1534561]

Hello Pradipta-san,

Thank you for your reply.

I understand that the Read/write operation to OSCEN bit is caused to increase power consumption, but it will not affect the normal read/write operations on the memory array.

If the host program accesses the RTC registers, I encourage customers to fully evaluate their power consumption.

I will close this discussion.

Best Regards,

Naoaki Morimoto