L15 – Digital I/O

1. ECE 2560 L15 – Digital I/O Department of Electrical and Computer Engineering The Ohio State University ECE 3561 - Lecture 1

2. Digital I/O on the 430 • Digital input and output • The ports • Port setup • The control registers • Using a port ECE 3561 - Lecture 1

3. The MSP 430 • The MSP 430 is a microcontroller intended for use in embedded systems. • As such, it needs to be capable of being connected with various input sensors and generating signal with control outputs. • For a large number of these, digital I/O is appropriate. ECE 3561 - Lecture 1

4. Digital I/O overview • A MSP430 device may have up to 6 digital I/O ports, P1 through P6. • Each port has 8 I/O pins. • Pins are configurable for input or output direction and each I/O line can be individually read or written to. • Ports P1 and P2 have interrupt capability with the interrupt for each I/O line individually enabled and configured. • All P1 lines source a single interrupt vector • P2 lines source a single interrupt vector (different than the vector for P1) ECE 3561 - Lecture 1

5. Summary of features • Digital I/O features • Individually programmable I/Os • Any combination of input or output • Individually configurable P1 and P2 interrupts • Independent input and output registers ECE 3561 - Lecture 1

6. Digital I/O • Digital I/O is configured with user software • Done by setting the value in port control registers. • Input register – a bit for each pin - PxIN • Bit = 0 – The input is low • Bit = 1 – The input is high • Output register – the value to be output on the pin - PxOUT • Bit = 0 – Set output low • Bit = 1 – Set output high ECE 3561 - Lecture 1

7. The control registers • Direction Register PxDIR • This register for a port sets the direction of each pin of the input/output port • Bit = 0 – The port pin is set to input direction • Bit = 1 – The port pin is set to output direction • Function Select Register – PxSEL • The ports can also be used with other peripheral devices according to the data sheet of the device. Or it is a simple I/O port. • Bit = 0 – Set function to I/O • Bit = 1 – Set peripheral function mode. ECE 3561 - Lecture 1

8. Interrupt Control Register (cont) • Interrupt Flag Registers P1IFG, P2IFG • For ports 1 and 2 these registers record if an interrupt is present on the appropriate pin. • Bit = 0 – No interrupt is pending • Bit = 1 – Interrupt is pending • Interrupt Edge Select Register P1IES, P2IES • These registers select whether the interrupt occurs on a rising edge or falling edge. • Interrupt Enable P1IE, P2IE • Each P1IE bit enables the associated PxIFG interrupt flag. (1 = enabled, 0 = disabled) ECE 3561 - Lecture 1

9. Unused Ports • What to do with the pins for unused ports? • Unused I/O pins should be configured as I/O function, output direction and left unconnected on the PC board. ECE 3561 - Lecture 1

10. Register summary • Port P1 • REGISTER Name Address Type • Input Register P1IN020h R • Output Register P1OUT 021h R/W • Direction Reg P1DIR 022h R/W • Interrupt Flag P1IFG 023h R/W • Intr Edge Select P1IES 024h R/W • Interrupt Enable P1IE 025h R/W • Port Select P1SEL 026h R/W • Internal Resistor P1REN 027h R/W ECE 3561 - Lecture 1

11. Register summary • Port P2 • REGISTER Name Address Type • Input Register P2IN028h R • Output Register P2OUT 029h R/W • Direction Reg P2DIR 02Ah R/W • Interrupt Flag P2IFG 02Bh R/W • Intr Edge Select P2IES 02Ch R/W • Interrupt Enable P2IE 02Dh R/W • Port Select P2SEL 02Eh R.W ECE 3561 - Lecture 1

12. Port 3 and 4 • Port P3 • REGISTER Name Address Type • Input Register P3IN 018h R • Output Register P3OUT 019h R/W • Direction Reg P3DIR 01Ah R/W • Port Select P3SEL 01Bh R/W • Port P4 • REGISTER Name Address Type • Input Register P4IN 01Ch R • Output Register P4OUT 01Dh R/W • Direction Reg P4DIR 01Eh R/W • Port Select P4SEL 01Fh R/W ECE 3561 - Lecture 1

13. Ports 5 and 6 • Port P5 • REGISTER Name Address Type • Input Register P5IN 030h R • Output Register P5OUT 031h R/W • Direction Reg P5DIR 032h R/W • Port Select P5SEL 033h R/W • Port P6 • REGISTER Name Address Type • Input Register P6IN 034h R • Output Register P6OUT 035h R/W • Direction Reg P6DIR 036h R/W • Port Select P6SEL 037h R/W ECE 3561 - Lecture 1

14. EXAMPLE OF use • On the launchpad there are 2 Light Emitting Diodes on the PC board • These are (according to the notation on the board) at P1.0 and P1.6 • Let’s turn then on and off ECE 3561 - Lecture 1

15. The steps • Configure the port • Port 1 • Configure the data direction register, P1DIR • Located at address 022h • Set value to 1 for output • Desire pins 0 and 6 of the port as output so value to set is 1xxxxx1x or just set it to all 1s • Instruction mov.b #0x0FF,P1DIR • Configure the interrupt enables to disable • Mov.b 0x00,P1IE ECE 3561 - Lecture 1

16. A note on code composer • As this MSP430 does have Port 1 the pneumonic labels such as P1OUT are defined in Code Composer. That is why they are commented out in the sample code. ECE 3561 - Lecture 1

17. The code • ; Set up the port • mov.b #0xFF,P1DIR ;set P1 to outputs • mov.b #0x00,P1IE ;disable interrupts • mov.b #0x00,P1SEL ;all pins are I/O • ; move values to the port • mov.b #0x00,P1OUT • mov.b #0x0F,P1OUT • mov.b #0xF0,P1OUT ECE 3561 - Lecture 1

18. A loop to toggle to output • mov #0xFFFF,R6 ;# times to wait • tol dec R6 • jne tol ;busy wait • mov.b P1OUT,R4 • inv R4 • mov.b R4,P1OUT • jmp tol ECE 3561 - Lecture 1

19. Notes on code • Busy wait : a term applied to techniques to insert a timed wait into a program that performs no useful computation other than to wait for time to elapse or an event to occur. • This toggles the leds based on time. • The code to toggle them could be tuned to take slightly less cycles but that this not desired here. ECE 3561 - Lecture 1

20. Summary - Assignment • Try out the code • Add an inner loop to lengthen the time for each individual light. • No new assignment. ECE 3561 - Lecture 1