ECE2049: Embedded Computing in Engineering Design C Term Spring Lecture #7: More Digital IO

Transcription

1 ECE2049: Embedded Computing in Engineering Design C Term Spring 2018 Lecture #7: More Digital IO Reading for Today: Davies , Users Guide Ch 12 Reading for Next Class: Davies , Users Guide Ch 12 Lab #0 (on web): Due NOW!! Lab #1 (on Web) : Early sign-off bonus by Fri 1/26 (code submit 5 pm) Report, code due Tues /30 HW #2 (on Web): Due Fri day 1/26 (in class) EXAM #1 9 am Monday 1/29/2018 in AK-116 Last class: Configuring and reading from and writing to the digital IO ports on the MSP430F > Using bit-wise operations to configure the digital IO ports MSP430F5529 Basic Digital I/O >> 8 independent, individually configurable digital I/O ports -- Ports 1-7 are 8 bits wide, Port 8 is 3 bits wide >> Each pin of each port can be configured individually as an input or an output >> Each pin of each port can be individually read or written to Function Select Register: Sets function of each pin in the port (e.g. P4SEL) -- Bit = 0 = Pin selected for Digital I/O -- Bit = 1 = Pin not selected for digital I/O (multiplexed pin functions) Direction Register: Sets direction of each pin in the port (e.g. P2DIR) -- Bit = 0 = Corresponding pin is an Input -- Bit = 1 = Corresponding pin is an Output Input Register: Where input to the port is read from (e.g. P2IN) -- Bit = 0 = Logic low -- Bit = 1 = Logic high Output Register: Where data to be output from the port is written (P5OUT) -- Bit = 0 = Logic low -- Bit = 1 = Logic high Drive Strength: Sets drive strength of port (we will usually leave as default) --Bit = 0 = reduced drive strength (default) --Bit = 1 = full drive strength

2 Pull-up/down Resistor Enable: Enable internal pull resistors (we will use with --Bit = 0 = Not enabled (default) buttons) --Bit = 1 = Enabled (see User's Guide) >> All I/O port registers are memory mapped They have addresses! Read and write to the registers names (defined msp430x55x.h) as if they were C variables! From last class: Ex: Using CCS C configure Port 3 for digital I/O with Pins 1 and 0 as inputs and Pins 7 thru 4 and outputs. BRUTE FORCE WAY: Does NOT preserve settings for unused pins 2 & 3. P3SEL = 0; // P3SEL = b = ALL P3 pins selected for digital I/O P3DIR = 0xF0; // P3DIR = b = P3.7-4 = Outputs, P3.3-0 = Inputs BETTER WAY: Use bit-wise operators to save any settings pins 2 & 3 may have --Remember, AND with 0 to set a bit to 0, AND with 1 to leave bit alone --OR with 1 to set bit to 1 and OR with 0 to leave bit alone P3SEL = P3SEL & 0x0C; // P3SEL AND b = 0000 xx00b P3DIR = P3DIR 0xF0; // P3DIR OR b = 1111xxxxb P3DIR = P3DIR & 0xFC; // P3DIR AND b = 1111xx00b

3 Using pre-defined constants to avoid magic numbers >> In C, there is always multiple ways to implement the same functionality >> Some ways are accepted as representing better coding style Try to avoid magic numbers = fixed hard-coded numbers that appear in code without explanation of their meaning or purpose >> These values are pre-defined in the msp430f5529.h header file... we can just use 'em! BIT0 = BIT4 = BIT1 = BIT5 = BIT2 = BIT6 = BIT3 = BIT7 = BIT2 BIT3 = or ~(BIT1 BIT0) = NOT( OR ) = b From last lecture: Configured P3.1-0 as inputs and P3.7-4 as outputs. P3SEL = P3SEL & (BIT2 BIT3); // = 0000 xx00 P3DIR = P3DIR (BIT7 BIT6 BIT5 BIT4); // = 1111xxxx P3DIR = P3DIR & ~(BIT1 BIT0); // = 1111xx00

4 Ex: Now, read in from Port 3 Pins 1-0 and put a 1 on the output Pin 7-4 that corresponds to the binary code 0-3 on Pins 1-0. P3.4 should represent 0 and P3.7 should represent 3. Another Example: Now, write a function that reads the low nibble from P6 into a byte (use internal pull-up resistors), and another functions that outputs the complement of the low nibble of its input argument on P void portconfig() /* Setup P6.3-0 as digital IO inputs with pull-up resistors */ /* Setup P4.7-4 as digital IO outputs */

5 char in_p6() // Read in from port 6. Preserve only the low nibble) char inbits; // local variable inbits = return(inbits); // return the value inbits void out_comp_p4(char inbyte) char outbits; // Complement input value, inbyte outbits = // Shift low nibble left to bits 7-4 outbits = //output on P4.7-4 P4OUT = An example of calling these functions inside a main() main(). portconfig(); indata = in_p6(); out_comp_p4(indata); // indata is locally defined char Now you know how to configure Digital IO ports when given that the pins are to be inputs or outputs but how do you know?

6 Input or Output? Let's take a closer look at the digital IO devices on our lab board starting with the 4 multi-colored LED's... >> On what port and pins are these LEDs connected? (are they an input or output device?) --> Check board Schematics posted and/or look thru demo project P6.4 P6.2 P6.1 P6.3 How do the LED functions work?

7 void initleds(void) // Configure LEDs as outputs, initialize to logic low (off) // Note the assigned port pins are out of order test board // Red P6.2 // Green P6.1 // Blue P6.3 // Yellow P6.4 // smj Dec 2016 P6SEL &= ~(BIT4 BIT3 BIT2 BIT1); P6DIR = (BIT4 BIT3 BIT2 BIT1); P6OUT &= ~(BIT4 BIT3 BIT2 BIT1); >> In an application program like the demo project the digital I/O ports are used repeatedly. The application programmer wraps the specific port functionalities by placing the assignments to the port specific registers into useful C functions. void setleds(unsigned char state) // Turn on 4 colored LEDs on P to match the hex value // passed in on low nibble state. Unfortunately the LEDs are // out of order with 6.2 is the left most (i.e. what we think // of as MSB), then 6.1 followed by 6.3 and finally 6.4 is // the right most (i.e. what we think of as LSB) so we have // to be a bit clever in implementing our LEDs // // Input: state = hex values to display (in low nibble) // Output: none // // smj, ECE2049, 27 Dec 2015 unsigned char mask = 0; // Turn all LEDs off to start P6OUT &= ~(BIT4 BIT3 BIT2 BIT1); if (state & BIT0) mask = BIT4; // Right most LED P6.4 if (state & BIT1) mask = BIT3; // next most right LED P.3 if (state & BIT2) mask = BIT1; // third most left LED P6.1 if (state & BIT3) mask = BIT2; // Left most LED on P6.2 P6OUT = mask;

8 >> These functions are easy to manipulate and can be re-sued in other applications with same hardware >> main() is then a series of calls to functions whose names convey their purpose void main(void) // Stop WDT WDTCTL = WDTPW WDTHOLD; // Stop watchdog timer initbuttons(); initleds(); configdisplay(); configkeypad(); while (1) setleds(some_val);