MSP430 power on reset (POR) TIME

Neelima,

 

Do you have a specific device in mind? See this post for a bit more information:

 

http://e2e.ti.com/support/microcontrollers/msp43016-bit_ultra-low_power_mcus/int-msp430_champs/int-msp430_ww_fae_support/f/170/p/29166/101338.aspx#101338

 

-Jason

 

The link you provided doesn't work. I get the error "Group not found".

I am evaluating MSP430F2xx Series  and haven't finalized the device. But I am considering MSP430F2002 device. Could you please tell me the fastest CPU startup time for CPU to start executing the code, may be using the DCO ( I think this is the fastest way I can execute my code after POR) for this CPU.

 

Thanks.

-Neelima

 

 

The datasheet of the F2002 states:

During power up, the CPU begins code execution following a period of td(BOR) after VCC = V(B_IT--)+ Vhys(B_IT--).

So it depends on VCC (> 1.92V at most, but may be less) and td(BOR) which is given as 2000µs max - If the RST pin isn't held low for a longer period (then execution will start right after RST going high).

neelima c said:

may be using the DCO

No, WILL be using DCO, since anythign else (including configuring DCO for somethign faster than the default) can only be done through code, and you asked for the time to START executing code.

Thanks.I am talking about the POR when i connect the power to MCU first time and don't use the reset pin.  Can I assume that CPU startup time in this case is basically the td(BOR) and it has maximum value 2000us.

You said DCO requires initialization. So, which clock the CPU will use after the POR for the code execution.

 

Neelima

 

neelima c said:

So, which clock the CPU will use after the POR for the code execution.

The default configuration for the DCo registers is DCOx=3 and RSELx=7 (2x family users guide).
this means the startup frequency is in the range of 0.8..1.5MHz depending on VCC and device variation (20x1/2/3 device datasheet)

So, Can I assume the CPU startup time for the first time power to MCU is basically the td(BOR) and it has maximum value 2000us.

 

-Neelima

neelima c said:

Can I assume the CPU startup time for the first time power to MCU is basically the td(BOR) and it has maximum value 2000us.

Provided that VCC is instantly rising from 0 to max and there is no additional delay due to the reset pin, yes.

p.s.: the newer MSPs have a different nomenclature for the reset conditions.
There's BOR (Brown Out Reset) which happens on electrical power-on or after a critical drop on VCC. Or when the RST pin is pulled low.
Next one is POR (Power On Reset) which is almost identical, but does NOT reset the voltage supervisors nor does it clear the reset vector register history.
The last is PUC (Power Up Condition), which initializes most of the hardware but not everything (PUC does not clear the timer config and disable timer interrupts).

A BOR causes always a POR and a POR always causes a PUC, but not the opposite direction.

The tagging of the default values in the register descriptions shows which bits are set on PUC or only during POR or BOR (those values are in different brackets)