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CHAPTER - 6

EVOLUTION OF MSP430 FAMILY MICROCONTROLLERS

Table of Contents

S.No. Name of the sub-title Page No.

6.1 Introduction 60-62

6.2 Architectural features 62-65

6.2.1. Operating Modes 66-69

6.2.2. Principles for Low-power Applications 70

6.2.3. Peripherals 70-73

6.3 Electrical Characteristics 73-77

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6. EVOLUTION OF MSP430 FAMILY

MICROCONTROLLERS

6.1 Introduction

MSP430 microcontrollers are 16-bit; RISC based mixed signal

processors from Texas Instruments. These MCUs offer the lowest

power consumption and the perfect mix of integrated peripherals for

thousands of applications. Now-a-days, the complex system design for

various applications of diverse fields, like biomedical engineering

energy consumption is one of the critical design parameter. Similarly,

it needs much effort to achieve low power dissipation in all levels of

design process. The component and sub systems, where operation

requires low power will be chosen for the entire low power design

architecture. To address these critical questions, the TI has come up

with this ultra low power family of microcontrollers which have rich

features for low power system design. It is the platform of very low

power processors with high integration, which can be employed in

several applications like spirometers, pulse oximeters, blood pressure

monitors and heartbeat monitors. This MSP430 microcontroller was

introduced in late 1990s, which is a straightforward 16-bit processor

with Von Neumann architecture and was designed for low power

applications [47]. The MSP indicates that this is equally employed for

both analog and digital signal inputs. For this an ADC with a

resolution of 16-bits is employed.

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It is not always possible to consider only one number to

demonstrate the low power consumption. For e.g. F2013 draws

around 4.5mA of current when operating at a speed of 16MHz and

requires a maximum source voltage of 3.5V. By reducing the source to

a value of 1.8V, the current can be unable to fall at a value of 0.2mA

while accepting 1 MHz speed. In various applications, it is mostly

operated in standby mode with a typical current well below 1mA. Due

to the presence of DCO, MSP430 microcontroller can restart easily,

which reduces the overall power budget.

In the present market 4 types of MSP430 processors are

available. The letter present immediately after MSP430 indicates the

types of memory. If the letter is F, it indicates flash memory. If it is C,

it indicates ROM. For ASSP’s, the second letter indicates the type of

measurement. The different letters used for measuring different things

are listed below:

1. W for water measurement.

2. E for electricity measurement.

3. G for gain measurement in op-amps

For example MSP430X1XX indicates that, it is a general

purpose device for simple as well as complex versions for signal

processing. MSP430F2xx is a newer, general-purpose family which is

introduced in the year 2005. MSP430X3XX contains drivers for LCD’s,

which is now obsolescent.MSP430x3xx can drive for LCD’s up to 160

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segments. Many of them are ASSP’s and some of them are general

devices too.

In the present design the MSP430F1611 Microcontroller is used.

The preceding sections will discuss the architectural and other

significant features of this microcontroller.

6.2 Architectural Features

MSP430 controller consists of a 16-bit RISC CPU, clocking

devices and some other peripherals which are interconnected by a

Von-Neumann memory address bus (MAB) and memory data bus

(MDB). By inter connecting a modern CPU with memory mapped

analog, digital devices, it offers the feasibility of mixed-signal

processing. For portable applications, to increase the life of battery

this controller is combined with five low power modes. Maximum code

efficiency is obtained because of very powerful 16-bit RISC CPU, 16-

bit registers, constant generators etc. The DCO offers switching

between different modes with in 6µs interval. The architectural

features of MSP430 micro controller are shown in figure 6.1 and the

pin diagram of MSP430F1611 is shown in figure 6.2.

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The salient features of MSP430F1611 are outlined below:

I. Ultra low power

0.1µA current usage extends RAM life.

0.8μA real time clock mode.

250μA /MIPS active.

II. High performance

10-bit or 12-bit analog to digital converter with 200Kbps is used

for temperature measurement.

12-bit dual digital to analog converter.

Resistive elements are measured by Comparator-gated timers.

Supply voltage in-charge.

III. 16-bit RISC

It has huge register file, which avoids difficulty of operation.

Compact design lowers the power consumption and reduces the

cost.

Optimum design for latest high level programming.

It has seven addressing modes and 27 core instruction set.

It has the capability to manage the vector interrupts.

IV. In-system programmable Flash allows data logging, field

upgrades and flexible code changes

The MSP430 CPU has seven addressing modes and 16 registers,

which reduces the execution time of instruction. Four registers

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namely R0, R1, R2 and R3 are designated as program counter, stack

pointer, status register and a constant generator respectively. The left

over registers are used as general purpose registers. Other devices are

connected to CPU via data bus, address bus and control bus, which

are operated with the instruction set.

MSP430F161x microcontrollers are configured with several

devices, which are listed below:

1. Built-in 16-bit timer devices.

2. 12-bit analog to digital and dual 12-bit digital to analog

converters.

3. One or two USART interfaces.

4. I2C, direct memory access and 48 I/O pins.

This microcontroller offers RAM addressing extension for

memory-based applications and huge C-stack needs.

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Fig.6.1: Functional Block diagram showing the Architecture of

MSP430F1611

Fig.6.2: Pin Diagram of MSP430F1611

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6.2.1 Operating Modes

The MSP430 microcontroller has totally six modes of operation.

Among them one is active mode and other five are low-power modes

which are software selectable. Any device can be made to wake-up

from one of these five low-power modes. The six operating modes

which are configured are given below:

I. Active mode AM

In Active mode, all clock cycles are active and power consumption

will be high.

II. Low-power mode 0 (LPM0)

In this mode, the CPU is actually disabled and ACLK and SMCLK

signals are activated at the same time. MCLK is disabled.

III. Low-power mode 1 (LPM1)

In this mode also, CPU is disabled and the ACLK and SMCLK

signals are activated at the same instant. MCLK is disabled and if

DCO is not operated in active manner, it can also be disabled.

IV. Low-power mode 2 (LPM2)

In this mode CPU is disabled, MCLK & SMCLK are disabled. DCO’s

dc generator remains enable & ACLK remains in active mode.

V. Low-power mode 3 (LPM3)

In this mode CPU, MCLK and SMCLK and DCO’s dc generators are

disabled and ACLK signal is activated.

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VI. Low-power mode 4 (LPM4)

In this fourth mode CPU, ACLK, MCLK, SMCLK and DCO’s dc

generators are disabled.

Fig 6.3 depicts the graph drawn between operating modes and current

consumption of MSP430.

Fig.6.3: Typical Current Consumption of MSP430 Devices with

operating Modes

By including several mode control bits in status registers,

namely CPUOFF, OSCOFF, SCG0 and SCG1, the current operating

mode can be saved on the stack during ISR. It can be returned back

to same operating mode, if the value of SR is not changed at the

execution of ISR. It can be moved to another operating mode with the

change in saved value of SR inside the ISR stack. By using any

instruction we can access the mode control bits and stack. By

selecting mode-control bits, the chosen operating mode will be affected

immediately. Peripherals are disabled if clock is disabled with their

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individual control register settings. All I/O port pins & RAM /registers

remain constant. Wakeup is possible along all enabled interrupts.

The schematic representation of various operating modes for the

basic clock system is shown in Figure 6.4. From the schematic, it is

clear that in active mode, the CPU is active and all enabled clocks are

active. Whereas in low power mode 4, CPU and all the clocks are

disabled. Hence this mode is the lowest power mode.

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Fig.6.4: Schematic representation of various operating modes for

the basic clock system

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6.2.2 Principles for Low-Power Applications

To reduce the power utilization of MSP430, clock system is used

to increase the time period of LPM3 operating mode. The LPM3

requires very less power about 2µA and all interrupts are active. For

activating ACLK and CPU it uses a 32 KHz crystal oscillator clock.

The flow of program can be controlled and the processor can be

made active with the help of interrupts.

The switching of peripheral devices can be done whenever it is

needed.

Fast look-up tables and branching are employed instead of flag

polling and huge software computations.

Because of overhead, unnecessary function calling and frequent

usage of code can be avoided.

Unique CPU register cycles are employed for more usage of long

software subroutines.

6.2.3 Peripherals

The MSP430 microcontroller has a rich set of peripherals. These

peripherals are connected to the CPU through address, data & control

buses and can be handled using all instructions.

I. DMA controller

Direct memory addressing avoids the involvement of CPU in

the process of transferring information from one address to

another address inside the memory. In this case, CPU is kept in

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sleep mode and avoids unnecessary power consumption. Using

DMA, the throughput of a peripheral device can be increased.

II. Oscillator and system clock

The clocking system of MSP430F1611 series are supported

through clock modules which includes high-frequency crystal

oscillators, a 32768 Hz crystal oscillator and an internal DCO

generator. This clock system is especially applicable to battery

powered applications.

III. Brownout, Supply Voltage Supervisor (SVS)

Proper internal reset signaling can be made at the time of

power on & power off by using a brownout circuit. The supply

voltage supervisor continuously monitors the supply voltage.

When it drops lower than a user required level, the CPU starts

executing the code after resetting the device by employing

brownout circuit clock.

IV. Digital I/O

It has 6 ports designated as P1 to P6, each of them are of 8-

bit length. All the I/O ports are programmed individually. The

ports P1 & P2 offers the feasibility to select Edge interrupts.

V. Watchdog timer

A watchdog timer can be employed to restart a controlled

system after the occurrence of a software problem. The

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watchdog timer can be used for generating interrupts at

prescribed intervals.

VI. Hardware multiplier

A particular peripheral module can be employed to perform

multiplication operations. This module supports 8x8, 8x16,

16x8 and 16x16 bit multiplication. This module supports signed

& unsigned multiplication, division and accumulation of data.

The result can be immediately obtained after loading the data

into the registers. No extra clocking signals are needed.

VII. USART0 & USART1

These are two hardware modules used by MSP430F1611 to

perform serial data communication. Both of them support SPF,

I2C protocols and UART by employing double buffered

transmitting and receiving channels. They also support

addressing modes of 7-bit and 10-bit with master and slave mode

configuration. To increase throughput of a system 16-bit length

I2C data transfer mode with two dedicated DMA channels are

supported by USART0 and USART1

VIII. Timer_A3

It is a 16-bit counter or timer with 3 compare or capture

registers and supports numerous compare/captures, pulse width

modulated outputs and timing interval. During overflow condition,

each of compare or capture registers generate the interrupts.

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IX. Timer_B7

It is a 16-bit timer/counter with 7 capture or compare

registers and supports multiple capture/compares, interval timing

etc.

X. Comparator_A

It is particularly meant for supervision of battery voltage,

external analog signal monitoring, precise conversion from analog

to digital.

XI. ADC12

It supports very fast conversion of 12-bit data from analog-to-

digital. It is used to implement 12-bit SAR, sample control,

conversion & control for conversion of 16-bit words and for

generating refresh control signals.

XII. DAC12

It is a 12-bit voltage output DAC, R-ladder. It can be used

for 8-bit or 12-bit operations along with DMA. With DAC12

module, synchronous operations are performed by grouping

them.

6.3 Electrical Characteristics

Most MSP430 devices operate at 1.8 V to 3.6 V, so a typical 3V

supply is enough for proper functioning. Connecting the JTAG to

support device memory programming and debugging is also

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important. For majority of the devices, there are two possibilities:

standard four-wire JTAG or MSP430 MCU-specific Spy-Bi-Wire (SBW,

or two-wire JTAG). Both interfaces are acceptable for programming

and debugging the application code. The main advantage of the four-

wire mode is speed. The main advantage of the two-wire SBW mode is

reduced pin-connection requirements.

So, to understand the low power activities of this controller, the

electrical characteristics are always useful. The Figure 6.5 shows the

variation of the supply voltage range with the frequency during the

program execution and flash memory programming.

Fig.6.5: Voltage range with the frequency during the program

execution and flash memory programming

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The utilization of current in active mode with respect to

frequency can be found using following equation:

I (AM) = I (AM) [1MHz] * f (system) [MHz]

The utilization of current in active mode with respect to supply

voltage can be found using following equation:

I (AM) = I (AM) [3V] +210µA/V * (VCC-3v)

Fig 6.6 and 6.7 shows the low-level output characteristics

between voltage & current

Fig.6.6: Typical lowlevel output

voltage vs lowlevel output

current characteristics for

Vcc=2.2V

Fig.6.7: Typical lowlevel output

voltage vs lowlevel output

current characteristics for

Vcc=3V

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The curves indicate that the output current levels saturate for the Port

3.5 at an output voltage of 2 to 3 volts. It is also observable that with

increase in the voltage levels of Vcc, the saturation levels also changes.

The typical power consumption values for various low-power modes

are shown in the Table 6.1. From the Table it is clear that even in the worst

case of active mode for Vcc =3 V, the maximum power dissipation is around

600µA and the power dissipation for the low power mode 4 is only about 0.5

µA which is considered to be the lowest power consumption of the

microcontroller. But on average one can expect a minimum power

consumption of about 50µA of current only. This is reasonably good for

many biomedical and wires sensor applications. The leakage currents of the

Ports P1 to P6 are also very low with a maximum value of 50 ± nA.

Table 6.1: The typical power consumption values for various low-power

modes

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PARAMETER TEST

CONDITIONS

VCC MIN TYP MAX UNIT

I(AM)

Active mode, (see Note1) f(MCLK)=f(SMCLK)=1MHz,

f(ACLK)=32,768 Hz XTS=0, SELM=(0.1)

TA=-400C to

850C

2.2V 300 300

A

3V 500 600

Active mode, (see Note1) f(MCLK)=f(SMCLK)=4,096Hz,

f(ACLK)=4,096 Hz XTS=0, SELM=3

TA=-400C to

850C

2.2V 2.5 7

A

3V 9 20

I(LPM0)

Low-power mode, (LPM0) f(MCLK)=0 MHz,

f(SMCLK)=1MHz, f(ACLK)=32,768 Hz XTS=0, SELM=(0,1)

(see Note1)

TA=-400C to

850C

2.2V

50 60

A

3V

95 75

I(LPM2)

Low-power mode, (LPM2) f(MCLK)=f(SMCLK)=0MHz,

f(ACLK)=32,768 Hz, SCG0=0

TA=-400C to 850C

2.2V 11 14

A 3V 17 22

I(LPM3)

Low-power mode, (LPM3) f(MCLK)=f(SMCLK)=0MHz,

f(ACLK)=32,768 Hz, SCG0=1. (See Note 2)

TA=-400C 2.2V

1.3 1.6

A

TA=250C 1.3 1.6

TA=850C 3.0 6.0

TA=-400C

3V

2.6 3.0

TA=250C 2.6 3.0

TA=850C 4.4 8.0

I(LPM4)

Low-power mode, (LPM4)

f(MCLK)=0 MHz, f(SMCLK)=0MHz, f(ACLK)=0 Hz, SCG0=0

TA=-400C 2.2V

/3V

0.2 0.5

A TA=250C 0.2 0.5

TA=850C 2.0 5.0