There are many more peripherals in the MSP430 and applications that it would be fun to explore but a book has to come to an end and we are nearly there. However, I cannot finish without saying a little about the MSP430X.

I was originally attracted to the MSP430 for teaching because of its uniform 16-bit architecture: Both addresses and data are 16 bits wide, which makes it trivial to use any of the general-purpose registers in the CPU for either purpose. Calculations likewise are the same for data and addresses. This is undoubtedly elegant but limits the size of the address space to 2 ¹⁶ = 64K bytes. That is typical of an 8-bit microcontroller and it was inevitable that the demand for evermore functions in embedded applications would necessitate an expansion. The result is the MSP430X, which can address a megabyte of memory. I explain in this chapter how the additional memory is organized and describe some of the changes to the instruction set that were made to accommodate it.

As I mentioned in the section "Where Does the MSP430 Fit?" on page 16, there is no separate family for devices that contain the MSP430X CPU. There isn't even an "X" in the part number to distinguish them! You have to look at the brochure and deduce the presence of the MSP430X from the size of the memory. This seems a curious approach in this publicity-conscious era and was presumably chosen to emphasize the transparent, upward compatibility...