This document discusses memory mapped I/O, the MSP430 architecture including memory, CPU, and peripherals. It describes the MSP430 Launchpad development board and how to control the onboard LEDs and button using the general purpose input/output ports and interrupts. It provides examples of state machine programming and using timer interrupts to implement functions like recording the time of button presses.

1. memory mapped IO
Data BUS
data memory
CPU
program memory
pc
sp
ALU
LD r1, a
LD r2, b
ADD r1,r2
ST c
r0
r1
r2
r3
a
b
c
Address BUS
b0
b1
y = 0b00000001; // turn on red
y = 0b00000000; // turn off red
y = 0x00; // turn off red
y = 0x01; // turn on red

2. LAUNCHPAD DEVELOPMENT BOARD
Embedded Emulation
6-pin eZ430
Connector
Part and Socket
Crystal Pads
Power Connector
Reset Button
LEDs and Jumpers
P1.0 & P1.6
P1.3 Button
Chip
Pinouts
USB Emulator
Connection
• 16kB Flash
• 512B RAM
• 2 Timer_A3’s
• 8 Ch. Comp_A+
• 8 Ch. ADC10
• USCI
10

3. Copyright 2009 Texas Instruments
All Rights Reserved
www.msp430.ubi.pt
3
MSP 430 ARCHITECTURE
 Architecture Overview
 Memory
 CPU
 Peripherals

4. Copyright 2009 Texas Instruments
All Rights Reserved
www.msp430.ubi.pt
4
MSP430 ARCHITECTURE

5. Copyright
2009
Texas
Instruments
All
Rights
Reserved
www.msp430.ubi.pt
5
MEMORY
 Memory Data Size
Byte, Word, Long Word
Byte = 8 bits
Word = 16 bits
Long Word = 32 bits
 Memory Address
Address size = 20 bits
Total addresses = 220 = 1 M
Each address holds 8 bits
A byte requires one address
A word requires two address
A long word requires four
addresses
 RAM Memory
Random Access Memory,
Read/Write Memory,
Holds data as long as power is
applied
Used for changing data
 Flash Memory
Read/ Write memory
Holds information even after
the power is turned off
Used to store programs and
fixed data

6. MEMORY MAP
Interrupt Vector Table
Flash
Information
Memory
RAM
16-bit
Peripherals
8-bit
Peripherals
8-bit Special Function
Registers
0Fh
0h
0FFh
010h
01FFh
0100h
03FFh
0200h
0FFDFh
0C000h
0FFFFh
0FFE0h
MSP430G2553
010FFh
01000h
7

7. MSP430 CPU
R2
R3
R4
R5
R7
R8
R10
R9
R11
R12
R13
R6
R14
R15
R0 / PC (Program Counter)
R1 / SP (Stack Pointer)
R2 / CG1
R3 / CG2
R4
R5
R7
R8
R10
R9
R11
R12
R13
R6
R14
R15
20-bit
Address
16-bit
Data
Memory Map …
6
 16 Registers R0 – R15
 Each register holds 16
bits of information
 Special Registers:
PC, SP
 Registers are used for
temporary data
 PC provides program
memory addresses
 SP provides stack
memory addresses

8. MSP430 PERIPHERALS
 General Purpose I/O Ports
 Timers: 16-bit
 Watchdog Timer
 Serial Communication: I2C, SPI
 Analog to Digital Converter:
 8 Channel/10-bit 200 ksps SAR
 Comparator
 Reset

9. LAUNCHPAD OUTPUT PORTS
 Port P1 with configurable pins
 Green LED: P1OUT bit 6 (or pin 6)
 Red LED: P1OUT bit 0 (or pin 0)
 P1DIR = Register whose bits configure the
corresponding port pins for input and output.
 P1OUT = Register whose bits turn the
corresponding pins of port P1 on or off

10. memory mapped IO
Data BUS
data memory
CPU
program memory
pc
sp
ALU
LD r1, a
LD r2, b
ADD r1,r2
ST c
r0
r1
r2
r3
a
b
c
Address BUS
b0
b1
b6
y = 0x01; // turn on red
y = 0x41; // turn on both
y = 0x00; // turn off both
y = y | 0x01 // red on only
y = y & 0xFE // red off only

11. b0
b1
b6
y = 0b01000000; // turn on green, turn off red
y = 0b01000001; // turn on both
y = 0b00000000; // turn off both
y = y | 0b00000001 // red on, green no change
y = y & 0b11111110 // red off, green no change
y = y | 0b01000000; // green on, everything else no change
y = y | 0x40; // green on only
y = y & 0b10111111; // green off only, everything else no change
y = y & 0xBF; // green off only

12. CONTROLLING LAUNCHPAD PORTS
BIT6 = 01000000b;
BIT0 = 00000001b;
P1DIR = BIT6 + BIT0; // P1.6 and P1.0 outputs
P1OUT |= BIT6; // P1.6 on (Green LED)
P1OUT &= ~BIT6; // P1.6 off
P1OUT |= BIT0; // P1.0 on (Red LED)
P1OUT &= ~BIT0; // P1.0 off
P1OUT |= BIT6 + BIT0; // both on
P1OUT &= ~(BIT6 + BIT0); // both off
P1OUT ^= BIT6 + BIT0; // toggle both
#define BIT6 01000000b;
#define BIT0 00000001b;
#define BIT6 0x40;
#define BIT0 0x01;

13. PORT 1

14. LAUNCHPAD INPUT PORT
 Port P1 with configurable pins
 Press button is connected to pin 3 of port P1
 Button pressed = logic 0
Button released = logic 1
 P1DIR = Register whose bit 3 configures the
corresponding port pin for input. Set it to 0 for input.

15. CONTROLLING LAUNCHPAD INPUT PORT
BIT3 = 00001000b;
BTN = 00001000b;
P1DIR &= ~BIT3; // P1.3 as input
P1DIR = P1DIR & (~BIT3);
while (P1IN & BIT3 == BIT3) // Wait for button
// press at P1.3

16. BUTTON INTERRUPT
Main Program {
1. set up button
2. turn on button interrupt in P1
3. enable CPU interrupt
4. do other things
}
Interrupt Vectors
Interrupt Service Routine {
1. double check interrupt source
2. perform button press functions
3. reset button interrupt
}
button interrupt vector

17. STATE MACHINE PROGRAMMING
BUTTON CONTROL LED FLASHING EXAMPLE
Upon start up, both LEDs flashing with the same period
- When button is pressed, flash only the red LED
- When button is pressed again, flash only the green LED
- When button is pressed for a third time, reset (i.e. have both
LEDs flashing again)
- And so on...
Reset
R & G
R
G

18. STATE MACHINE EXERCISE
Reset
R & G
on
R only
G only

19. STATE MACHINE BUTTON
ISR DOES EVERYTHING
Main Program {
1. set up button
2. turn on button interrupt in P1
3. initialize to RG state
4. enable CPU interrupt
5. do other things
}
Interrupt Vectors
Interrupt Service Routine {
1. double check interrupt source
2. perform button press functions
3. update state and flash lights
accordingly
4. reset button interrupt
}
button interrupt vector
state
state declared as global so it
can be accessed by ISR

20. STATE MACHINE BUTTON
ISR DOES MINIMUM
Main Program {
1. set up button
2. turn on button interrupt in P1
3. initialize to RG state
4. enable CPU interrupt
5. loop forever
flashing lights based on state
}
Interrupt Vectors Interrupt Service Routine {
1. double check interrupt source
2. perform button press functions
3. update state
4. reset button interrupt
}
button interrupt vector
state
state declared as global so it
can be accessed by ISR
LED flashing has spin idle delay so it takes a while to finish, we
want ISR to be rapid so CPU can handle other interrupts if
necessary

21. TIMER INTERRUPT
Main Program {
1. set up timer
2. turn on timer interrupt
3. enable CPU interrupt
4. do other things
}
Interrupt Vectors
Interrupt Service Routine {
1. double check interrupt source
2. perform timeout events
3. reset timer interrupt (no need
in continuous mode)
}
timer interrupt vector

22. TIMER AND BUTTON INTERRUPTS
Main Program {
1. set up button
2. turn on button interrupt in P1
3. set up timer
4. turn on timer interrupt
5. enable CPU interrupt
6. do other things
}
Interrupt Vectors
Interrupt Service Routine {
1. double check interrupt source
2. perform button press functions
3. reset button interrupt
}
button interrupt vector
timer interrupt vector
Interrupt Service Routine {
1. double check interrupt source
2. perform timeout events
3. reset timer interrupt (no need
in continuous mode)
}

23. TIMER AND BUTTON INTERRUPTS
RECORD KEY PRESS TIME EXAMPLE
Main Program {
1. set up button
2. turn on button interrupt
3. set up timer
4. turn on timer interrupt
5. enable CPU interrupt
6. do other things
}
Interrupt Vectors
Button ISR {
1. double check interrupt source
2. record wall clock for each key
3. reset button interrupt
}
button interrupt vector
timer interrupt vector
Timer ISR {
1. double check interrupt source
2. perform timeout events
3. reset timer interrupt (no need
in continuous mode)
}
currentTime
wall clock, updated
by timer ISR
keyPressTime [0]
used by button ISR
keyPressTime [1]
keyPressTime [2]
keyPressTime [3]