Startup issues

radsdau · ‎2004-07-04

Posted on July 05, 2004 at 05:26

Startup issues

radsdau · ‎2003-10-05

Posted on October 06, 2003 at 01:23

Hi all,

I have a possible issue with oscillator startup on my ST10F168 app... occasionally I'll get a unit that doesn't start; I have to remove power and reapply it for it to work. Current statistics are about 95% of units work fine, and the rest have this odd behaviour about 5% of the time, a couple about 20% of the time.

I designed this originally from a PDF document that I cannot find again (most frustrating). So, if anyone would like to check this, the circuit details are below:

Crystal is 3.6864MHz, load Cs are 33pF, feedback R is 3.3Mohm, series R is 1k on XTAL2 pin.

Using x4 PLL internal to give 7456MHz Eclock.

Any suggestions / fixes / comments would be appreciated. Many thanks.

Rhys

charles239955_st · ‎2003-10-05

Posted on October 06, 2003 at 08:23

Hi.

I see 2 possibilities for this behavior.

1/ The RSTIN pulse is not held long enough for the oscillator to start and the PLL to lock. In that case the ST10 will anyway start but with a bad frequency as it will be clocked by the PLL free running frequency (around 5MHz).

2/ Check the Vpp pin connection. This pin is used to provide the 12V for Flash programming but also selects between 2 types of reset. To ensure a correct start of the ST10, this pin MUST be seen at the powering off the application. Otherwise the ST10 may be frozen in an undefined stage and only a power-off power-on sequence migth take it off this stage.

radsdau · ‎2004-07-04

Posted on July 05, 2004 at 00:09

Thanks Kenshin....

This is looking promising; other symptoms I've observed may be consistent with the VPP pin voltage, as you mentioned. I haven't read this detail before anywhere; can you please steer me to the right spot in the datasheet please, or send through the details?

najoua · ‎2004-07-04

Posted on July 05, 2004 at 05:26

Hello,

The VPP/RPD pin selects between two types of reset: Asynchronous and Synchronous Reset.

An asynchronous reset is triggered when RSTIN pin is pulled low while VPP pin is at low level.

The asynchronous reset must be used during the power-on of the MCU. Depending on crystal frequency,the on-chip oscillator needs about 10ms to 50ms to stabilize. The logic of the MCU does not need a stabilized clock signal to detect an asynchronous reset, so it is suitable for power-on conditions. To ensure a proper reset sequence, the RSTIN pin and the VPP pin must be held at low level until the MCU clock signal is stabilized and the system configuration value on Port0 is settled.

A synchronous reset is triggered when RSTIN pin is pulled low while VPP pin is at high level.

For more details, you can refer to the ''SYSTEM RESET'' part of the ST10F168 datasheet and to the following link:

http://www.stmcu.com/forums-cat-87-5.html

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Najoua