MSP430FR5739 implementing 2 crystals for RTC and UART

cuong nguyen1

If I need to use both the RTC and UART, do I need 2 crystals? Can I use just a 32khz crystal for the RTC and do a frequency multiplication for the UART with the fr5739 part?

Thanks,

Carl

over 13 years ago

0 Leo Hendrawan over 13 years ago

TI__Guru 56650 points

Hi,

you can use even the internal calibrated DCO as the clock source for the UART.

Please refer to the MSP430FR57xx Family User's Guide - http://www.ti.com/lit/ug/slau272a/slau272a.pdf - Table 18-5. Recommended Settings for Typical Crystals and Baudrates at page 436. There you can find that even using the internal DCO clock, you can achieve relatively very low error percentage on UART communication.

I hope this helps.

0 cuong nguyen1 over 13 years ago in reply to Leo Hendrawan

Intellectual 540 points

I see Table 18-5. Recommended Settings for Typical Crystals and Baudrates. Is the BRCLK frequency referring to te crystal frequency or the DCO frequency?

0 Leo Hendrawan over 13 years ago in reply to cuong nguyen1

TI__Guru 56650 points

Hi,

i think you need the 32kHz for the RTC module, but not for the UART. Please refer to the MSP430FR57xx Family User's Guide, SLAU272 - chapter 3 (especially look at the block diagram shown in Figure 3-1).

0 cuong nguyen1 over 13 years ago in reply to Leo Hendrawan

Intellectual 540 points

Table title says Table 18-5. Recommended Settings for Typical Crystals and Baudrates

So is the BRCLK in the table referring to the crystal frequency or the DCO frequency? I was checking the error rate but wasn't sure if it was the error rate for different crystals or different DCO frequencies.

0 Leo Hendrawan over 13 years ago in reply to cuong nguyen1

TI__Guru 56650 points

Hi,

the BRCLK in Table 18-5 is basically input clock frequency of the eUSCI module. Please refer to the Figure 18-1. "eUSCI_Ax Block Diagram – UART Mode (UCSYNC = 0)." in the same document.

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MSP430FR5739 implementing 2 crystals for RTC and UART