hercules external oscillator questions

Hello Brian,

I have forwarded your post to one of our experts.  They will respond back soon.

Brian,

The external oscillator is driving a 3.3V peak-to-peak signal into OSCIN and OSCOUT is left open, right? In that case, Kelvin_GND is tied to the external oscillator's ground (which should be common to other grounds on the device).

I'm not sure I follow the question about the real-time clock.

 - The part does not have a crystal driver targetted for a 32KHz oscillator.

 - An internal RTI block can be clocked by a variety of clock sources, including the oscillator you drive into OSCIN.

Best Regards,

Kevin Lavery

Brian,

The biggest issue with trying to implement a RTC on the TMS570 is going to be the leakage power due to the 65nm node that it's implemented on.

It's not listed separately in the datasheet, but there are some formulas at the bottom of the table with the ICC specs that explain how to calculate the expected current at different frequencies and temperatures. I believe this will work out to low mA not <100uA like you might expect from an RTC function.

Your best bet is to use a separate RTC chip if you want a low power time of day function.

TI makes some RTC chips w. battery backup, list is here:  http://www.ti.com/lsds/ti/clocks-timers/real-time-clocks-products.page

Or, you could use a low cost MSP430 as an RTC chip as described in this appnote.  I think this can be made to work on the value-line parts which are very inexpensive.  This would also give you some additional programmability in the system to say manage other power domains.

-Anthony

Thank you! One more question. We need clarification on and that is the pinouts for the I/O ports GIOB, GIOC, GIOD, DIOE, and GIOF so that we may group our signals accordingly. The user guide indicates that these ports are defined in the data sheet, but the data sheet only lists the pins for GIOA.

-Brian

Brian,

The device has only the GIO ports available that are listed in the datasheet, so depending the device at present this would be GIOA and possibly some/all of GIOB.

The IP that is documented in the TRM could support additional ports, but most devices don't make use of these.   Almost all of the peripherals on the device support GIO mode for their pins, so the central GIO controller really only adds external interrupt capability.

So if you need additional GIO you could use pins from N2HET, DCAN, SCI/LIN, MIBSPI.   Look for the pin control registers in each of the TRM chapters and you can see what capability is there.   Most of the peripherals make you select between GIO mode and functional mode in one register.   Many allow you to use some of the pins as GIO and some as  functional.   For example the SPI might have four or five chip select pins but you can decide to use none or say only one or two as chip selects and use the rest as GIO. 

N2HET pins are always avaialble as GIO *and* N2HET simultaneously,  so the N2HET can take an action to set a pin but the CPU could come in and clear the pin in an ISR,  without changing any 'mode' of the pin.

The main exceptions where the modules don't include GIO capability are EMIF, Etherent, USB and I think flexray.   But a lot of times these pins are muxed with another module that does include GIO support;  so most pins can be used as GIO.

Best Regards,

Anthony