msp430f4132: From a hardware guy, leaving no loose ends.....

Hi Robert,

Thanks for posting. I'm assuming you're doing a hardware layout and you're trying to make sure that your pin selections aren't going to cause a conflict or issue for the software? Looking in the MSP430F4xx Family User's Guide www.ti.com/lit/pdf/slau056 section 25.2.5 LCD Outputs, there is a description of how the multiplexing of pins with LCD functions is handled in this family of parts (note for others: this may be different on later MSP430 families like F6xx or FR6xx - check their respective user guides).

4xx user's guide said:

The pin functions for COMx and Rxx, when multiplexed with digital I/O, are selected using the applicable PxSELx bits as described in the Digital I/O chapter. The LCD segment functions, when multiplexed with digital I/O, are selected using the LCDPx bits.

The LCDPx bits selects the LCD function for groups of pins. When LCDPx = 0, no multiplexed pin is set to LCD function. When LCDPx = 1, segments S0 to S15 are selected as LCD function. When LCDPx > 1, LCD segment functions are selected in groups of four. For example, when LCDPx = 2, segments S0 to S19 are selected as LCD function.

So you can select some pins to be LCD function and some pins to be other function, without having to do this quick switch that you are talking about - it will depend on how many LCD segments you need for your display. As you can see from the description, the minimum selection of LCD pins is going to be S0-15, so I would recommend avoiding those pins entirely for any other function - indeed, checking the MSP430F4132 datasheet, most of these pins are only muxed with GPIO, aside from some timer outputs that are available on some other pins as well. For any more segment pins you need beyond S0-15, you are limited in that you can only add additional LCD pins in groups of 4 and it will always be in a contiguous block down to S0. This may mean you have a few unused pins that have to be selected as LCD function simply due to the granularity of LCDPx only being in groups of 4 pins. If possible, I would recommend using other GPIOs for your other functions that are not going to be selected for LCD function by your needed LCDPx setting.

Does this present a conflict with any of your functions - if so maybe we can discuss this if you can share what other functions will cause problems, how many segment pins you need for the LCD, etc.

One more note: when selecting what Sx pins on the MSP to connect to particular segment pins on your LCD display, I strongly recommend reading through chapter 5 of this application note Designing with MSP430 MCUs and Segment LCDs www.ti.com/lit/pdf/slaa654 - you have an opportunity in your hardware connection selection to ensure that the software for displaying data on the LCD can be as efficient and simple as possible.

Regards,

Katie