CPU Registers

3.2.2Stack Pointer (SP)

The stack pointer (SP/R1) is used by the CPU to store the return addresses of subroutine calls and interrupts. It uses a predecrement, postincrement scheme. In addition, the SP can be used by software with all instructions and addressing modes. Figure 3−3 shows the SP. The SP is initialized into RAM by the user, and is aligned to even addresses.

Figure 3−4 shows stack usage.

Figure 3−3. Stack Pointer

15

1

0

Stack Pointer Bits 15 to 1

0

MOV

2(SP),R6

; Item I2 −>

R6

 

MOV

R7,0(SP)

; Overwrite

TOS

with R7

PUSH

#0123h

;

Put 0123h

onto TOS

POP

R8

;

R8 = 0123h

 

 

Figure 3−4. Stack Usage

Address

0xxxh 0xxxh − 2 0xxxh − 4 0xxxh − 6 0xxxh − 8

I1

I2

I3

PUSH #0123h

 

POP R8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I1

 

 

I1

 

 

 

 

 

 

 

 

I2

 

 

I2

 

SP

 

 

 

 

 

I3

 

SP

I3

 

 

 

 

0123h

 

0123h

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SP

The special cases of using the SP as an argument to the PUSH and POP instructions are described and shown in Figure 3−5.

Figure 3−5. PUSH SP - POP SP Sequence

PUSH SP

SPold

SP1 SP1

POP SP

SP2 SP1

The stack pointer is changed after a PUSH SP instruction.

The stack pointer is not changed after a POP SP instruction. The POP SP instruction places SP1 into the stack pointer SP (SP2=SP1)

RISC 16-Bit CPU

3-5

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Texas Instruments MSP430x1xx manual Stack Pointer SP, 3. Stack Pointer
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MSP430x1xx specifications

The Texas Instruments MSP430x1xx series is a family of ultra-low-power microcontrollers that are highly regarded in the embedded systems community for their versatility and performance. Designed for applications ranging from portable instrumentation to low-power industrial devices, the MSP430x1xx combines flexibility and efficiency with advanced features tailored for energy-sensitive applications.

One of the standout characteristics of the MSP430x1xx is its ultra-low-power operation. This series offers several low-power modes that can significantly extend battery life in portable devices. The microcontroller can be in active mode, low-power mode, or even in a deep sleep state, allowing developers to optimize power consumption based on the application's requirements. In fact, some configurations can operate at just a few microamps, making it ideal for battery-operated devices.

Another key feature is the 16-bit RISC architecture that provides powerful processing capabilities while maintaining a low power profile. The MSP430x1xx series supports a maximum clock speed of 16 MHz, allowing for efficient task execution while consuming minimal energy. This architecture ensures that programs run smoothly while the microcontroller remains energy efficient.

The MSP430x1xx is equipped with various integrated peripherals, including analog-to-digital converters (ADCs), timers, and communication interfaces like UART, SPI, and I2C. The inclusion of a powerful ADC enables the microcontroller to handle sensor readings with high accuracy, making it suitable for applications like environmental monitoring and medical devices. The integrated timers provide essential functionality for real-time applications, allowing for event-driven programming and precise timing control.

Memory options in the MSP430x1xx series are also robust, with configurations offering flash memory sizes from 1 KB to 64 KB. This flexibility allows developers to choose the optimal memory size for their specific applications, accommodating a wide range of requirements.

Additionally, the MSP430x1xx microcontrollers are designed with a wide operating voltage range, typically from 1.8V to 3.6V, making them compatible with various power sources and further enhancing their usability in diverse applications.

In summary, the Texas Instruments MSP430x1xx series of microcontrollers is an excellent choice for developers seeking low-power, high-performance solutions for embedded applications. With an efficient architecture, a rich set of peripherals, and flexible memory options, these microcontrollers are positioned to meet the growing demands of modern electronic designs, particularly in battery-powered and energy-sensitive applications.
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