Electronic – How critical a resistor value for MSP430 spy-bi-wire on reset

msp430

When setting up a circuit for the TI MSP430 – the reset line in all example circuits has a 47k Ohm resistor (R1 below) on it. How critical is that specific value and why that value?

This is what I've currently been using to do this.

Can I use something else higher or lower? 47k isn't an SMD part I have on hand typically.
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Best Answer

I would expect that several factors will put constrains on the size of the pull up resistor:

It must be big enough such JTAG driving circuit (programmer/debugger) will be able to override it,
It must be small enough that leakage current/noise will not change logic value of the line,
The RC constant that remove /RST after supply ramp up will have to be chosen to ensure proper reset.

Check documentation of uC and JTAG programmer for leakage and drive strength. Based on that size your pull up resistor. I would try to keep RC constant the same which would mean re-sizing capacitor. Note however that schematic you posted put maximum restriction on the capacitor to 2.2nF.

Standard disclaimer: You should follow manufacturer recommendation. There is good reason for that as good gals and guys that made the chip may have put really strange things into it (that are just waiting to bite you). What is worst such things may not be documented as describing them would reveal trade secret. If needed contact your support channel (usually not possible for small customers or DIYers - in this case experiment!). Note that I am not affiliated with TI and I do not have "inside" knowledge of the device.

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Electronic – Debugging initialization of LCD with NT7605 driver

Oh, duh, I didn't read your code carefully -- your send SendLcdByte is wrong:

    void SendLcdByte( unsigned char command_0_or_data_1, unsigned char command)
{
    SendLcdUpperNibble( command_0_or_data_1, command);
    // send the lower nibble next
 // AS WRITTEN:
    P1OUT = (command & 0x0F) | (P1OUT & 0xF0);
 // SHOULD BE:
    P1OUT = ((command & 0x0F) << 4) | (P1OUT & 0xF0);
    Strobe( command_0_or_data_1);
}

Electronic – Spy-Bi-Wire vs JTAG

Spy-Bi-Wire is JTAG - the physical layer is just different. JTAG is a set of commands over a serial interface. The main problem is the chip you're debugging. The chip you're debugging has to have the support for the fancy features - not just your JTAG. And indeed, in TI's own documentation for the JTAG interface on MSP430 it spells out how its chips don't fully implement all JTAG commands (section 3.2, pg 67):

Only the BYPASS instruction is supported. There is no support for SAMPLE, PRELOAD, or EXTEST instructions.

Here's the fun part: since Spy-Bi-Wire is just serial communication, all of the actual cool features have to be implemented on the MSP430. For instance, the number of hardware breakpoints you have? Determined by the processor, not the JTAG you're using. Most MSP430's have two, some have eight.

Best Answer

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