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msp430f5438a connect XT2 to ACLK

Cat cart
Prodigy 70 points

Other Parts Discussed in Thread: MSP430F5438

Hey, I'm using the TRxEB development board which features the MSP430f5438. I've connected a 20Mhz crystal to the XT2 pins (p5.2, p2.3). here is what I did to active it:

// set up the clock
UCSCTL4 = ( UCSCTL4 & (~0x0700) ) | 0x0500; // ACLK <- XT2
UCSCTL6 = ( UCSCTL6 & (~0xFF00) ) | 0x8000; // XT ON & 20Mhz
P5SEL |= BIT2 | BIT3; // select custom function (XTL)

// I've set up a timer interupt and inverted a pin to check the frequency
TA0CCR0 = 1000;
TA0CCTL0 = CIEE; // run up to 1000
TA0CTL = TASSEL1 + MC_1; // USE ACLK & UP MODE

The interrupt occures once evey ~1ms which is probobly not becuuse of my 20Mhz clock, but becuse some other 1MHZ clock that's connected to the ACLK.

MOREOVER, even if I dont do my clock init stuff, I still get that ~1ms

What am I doing wrong? how do i connect the XT2 crystal clock to the ACLK?

  • 0
    TI__Guru 56650 points

    Hi,

    could you check whether your XT2 is failing? You can do this via XT2OFFG bit of UCSCTL7 register.

  • 0 in reply to Leo Hendrawan
    Prodigy 70 points

    I always read the XT2OFFG as '1'. So as I understand It's not running, I've tried a few diffrent quartz crystal oscilators, which I mounted on the P5 on the TRxEB board.

    strangly when I mesure the crystal I DO see the oscilatons, so the crystal is working, it's just the chip, doesn't want to use it

    non of them seems to work see schematic:

    http://e2e.ti.com/cfs-file.ashx/__key/telligent-evolution-components-attachments/00-155-01-00-00-67-19-37/TrxEB_5F00_1_5F00_7_5F00_0_5F00_Reference_5F00_Design.zip

  • 0 in reply to Cat cart
    Guru 227245 points

    Did you follow the init procedure described in the users guide? At power-on, the crystal is not oscillating. So a fault is generated. You can only switch to the crystal after all fault bits are clear (including OFIFG). Until then, (partly) fallbacks are used. See the users guide about fail-safe operation.

    However, for operating a crystal, you’ll need the proper load capacitance. (a load of 10pF means two 20pF capacitors, minus 1pF for pin capacitance and maybe one or two more for trace capacitance) Also, it has to be mounted as close as possible to the MSP and all traces to connectors need to be cut. Else the oscillation is not reliable and may even fail to be recognized by the fault detection. (this doesn’t apply for a self-powered oscillator with TTL clock signal output).

    Apparently, your ACLK still runs from DCO with its default 1MHz.

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