0.5 Lab 3-2 digital input and lab 3-2 output with the msp430 (escape

Basic digital i/o in the real world

In this lab you'll go over the basics of how to setup and use the GPIO on the MSP430. This will allow you to get data from the outside world, run some processing on it, and then output it again as useful information. You only have one task this week:

1. Coding in MSP430 assembly, write a simple I/O echo program . Setup the GPIO pins and poll the input DIP switches for any changes. Take the input and display it to the output so any changes are immediately reflected. Step through this program to observe how it behaves. Assignment Details

Digital i/o basics

Gpio

Philosophy

• The MSP430 uses a limited number of GPIO hardware pins that are assignable to several functions depending on your specific model and your program's needs. For example, our version, the MSP430F5637, can have the pins act as digital output, digital input, or ADC input.
• The pins are organized into ports, with each port usually one byte (8 bits/pins) wide. On larger versions of the processor (different format chips with physically many more pins...) you can encounter several ports. In this lab our MSP430F5637 has 9 different ports we will use.
• You can set each pin's function independently (input or output) by modifying some memory mapped I/O registers. Since we want to do both, we will assign different tasks to different pins as needed.

Usage

• The I/O ports are memory mapped into the top of the MSP430 address space.
• There are several registers associated with each port. For now, you only need to worry about six (P4IN, P4OUT, P4DIR, and P9IN, P9OUT, P9DIR).

  P9in

  • The P9IN register is located in memory, which you can refer to using the C symbol &P9IN
  • The register holds the values the MSP430 sees at each associated pin, regardless of the pin direction setting.
  • To read the register, it is good practice to use a mov.b instruction to avoid accidentally reading adjacent registers
  • If you are looking to test or read just the pins set to input, you will have to mask the P9IN register to zero out the other unwanted/output pins. Reading P1IN reads the entire port, regardless of pin direction.

  P4out

  • The P4OUT register is located in memory, which you can refer to using the C symbol &P4OUT
  • If their direction bits in P4DIR are set to output/ "1", the corresponding pins will output the values set in P1OUT.
  • If a pin's direction bits are set to input in P4DIR and its resistors are enabled in P4REN, P4OUT controls the pin's connection to the pull-up resistor. Setting P4REN to "1" enables the pull-up, while setting it to "0" leaves the input to float in a high impedance state.
  • To set P1OUT, use a mov.b instruction to set several pins at once. To set individual bits to "1", you can use an or.b instruction with a "1" in the positions you want to set. To clear individual bits/ set them to zero, use an and.b instruction with mostly "1"s except for a "0" for the bits you want to clear.

  P4dir

  • The P4DIR register is located in memory, which you can also refer to using the C symbol &P4DIR
  • The value of the bits in P4DIR determines whether the MSP430 hardware leaves the pin in a high impedance state where it responds to external voltage changes (which you can read at P4IN), or in a low impedance state where the MSP430 drives the output voltage to a certain value determined by P1OUT.
  • To set the bit directions all at once, use a mov.b instruction, but to change individual bits regardless of the others, use an and.b or a or.b
  • Set the corresponding bits to "0" to set pins to input mode, or to "1" to set them to output mode.