Semester 1. Module Code: EEE305J1. Module Title: MICROCONTROLLER SYSTEMS

Transcription

1 UNIVERSITY OF ULSTER UNIVERSITY EXAMINATIONS : 2004/2005 Semester 1 Module Code: EEE305J1 Module Title: MICROCONTROLLER SYSTEMS Time allowed: 3 Hours Answer as many questions as you can. Not more than TWO questions from Section B will contribute to the final mark. A PIC instruction set and CCS C compiler reference set appears at the end of this paper. 1/9 Module Co-Ordinator: Dr S J Katzen

2 SECTION A Q.A1 A dedicated PIC16F84-based microcontroller is to be designed as an intruder alarm to continually monitor the state of four sensors at various points in a building. Each of these acts as a 2-state device, giving a high (logic 1) or low (logic 0) voltage as defined below. The system output is to be a 4-LED array with flashing lights showing which sensor is active and a single siren if any movement sensor is active. You are asked to design the hardware and software which will: Read the bank of four sensors Activate the appropriate LEDs if sensors are active. Activate the siren alarm for a minimum period of 30 seconds. Repeat the above continually. Pertinent hardware details are: The intruder sensors output a logic 1 when activated. Each LED requires a nominal 10mA to illuminate. The siren is activated via a relay activated directly from +5V. The PIC16F84 is clocked using a 1MHz crystal and is powered using a +5V supply. You are required to design both input and output interface for the sensors, LEDs and buzzer/relay and software to implement the scheme. Answers (1) through (3) should be illustrated with a diagram and any necessary Parallel port configuration shown at that point in your answer. (1) The input interface for the four sensors. [5 marks] (2) The output interface for the four LEDs. Determine the value of the current limiting resistors and state if your connection illuminates with a logic 0 or logic 1 (low or high). [8 marks] (3) A single output line to drive the buzzer. [2 marks] (4) A flow chart on task list and assembly-level coding implementing the software specified below. You can assume that all locations between File h 20 and File h 2F are available for general storage. (a) A main routine to: (i) initialise the system; 2/9

3 (ii) (iii) check the state of the sensors continually until an intruder is sensed; flash the appropriate LED(s) on and off at a nominal 1Hz rate for a total duration of 30 seconds whilst sounding the siren; (iv) disable the warning devices and repeat indefinitely; [32 marks] (b) A subroutine giving a nominal fixed delay of 0.5s based on the 1MHz crystal. You must show your calculations for full marks. [13 marks] For bonus marks. (5) How might you go about expanding the system, say, to cope with up to eight sensors in a zone and up to four zones? [6 marks] (6) Rather than using discrete LEDs to indicate active sensors, how might you display the sensor number as a decimal digit? What hardware and software changes would have to be made? [4 marks] 3/9

4 SECTION B Q. B2 (a) Software targeted to Microcontroller systems is coded either at assembly level or using a high-level language; typically C. Discuss the advantages and disadvantages of each approach. [3 marks] (b) A certain petrol tank capacity detector uses a digital pressure transducer whose naturally coded 8-bit output can be read by a PIC MCU at Port B and varies linearly from zero (empty, b ) to 255 (full, b ). Four LEDs and a buzzer are connected to Port A to act as a petrol gauge according to the following scheme: Green (Port A, pin 0) : Amber (Port A, pin 1) : Over ½ full Over ¼ and up to ½ full Red (Port A, pin 2) : ¼ full or under Buzzer (Port A, pin 3) : Under 1/8 full Design and implement a function in the C language that will set up Ports A and B appropriately and activate the indicators as listed. A CCS C compiler reference set is given at the end of the paper. [17 marks] Q. B3 (a) The ASCII code for the symbol C is h 43. If this character is to be transmitted using the asynchronous serial protocol at 1200 baud with eight data bits, no parity and one stop bit, draw a waveform annotated clearly with time and voltage that represents what you would observe monitoring the signal using an oscilloscope from (i) the transmit line from the UART, (ii) the RS232 transmit line. [14 marks] (b) If a device receiving an asynchronous transmission is incapable of processing the incoming data fast enough, several techniques can be employed to allow the receiver to slow down the transmission character rate; these involve hardware and software handshake techniques. Discuss, with the aid of diagrams, either of these methods. [6 marks] 4/9

5 Q. B4 (a) Digital to analog convertor (DAC)s are used to convert a digital word to an analogue equivalent. Thus an 8-bit DAC can transform a digital byte to one of 256 possible levels. Describe one method of conversion. [6 marks] (b) An 8-bit DAC is to be used to in conjunction with an analog comparator to implement an analog to digital convertor process. The digital input to the DAC is derived from Port B of a PIC MCU. The analog output from the DAC is in turn connected to one input of the analog comparator, with the analog input voltage connected to the other input. The digital output of the comparator is fed back to pin RA0 of Port A. Show how this circuit may be used to convert from analog to digital in eight steps. Design software to implement this successive approximation algorithm, as a subroutine returning with an 8-bit digitized equivalent of the input analog voltage. [14 marks] 5/9

6 14-bit 16CXX Dest CCR op-code Instruction Mnemonic WFZD C Operation summary LLLL LLLL ADD Literal to W addlw LL w <- w + #LL dfff ffff ADD W and F addwf f,d d <- w + f LLLL LLLL AND Literal to W andlw LL w <- w #LL dfff ffff ANDWtoF andwf f,d d <- w f 01 00nn nfff ffff Bit Clear File bit n bcf f,n 01 01nn nfff ffff Bit Set File bit n bsf f,n 01 10nn nfff ffff Bit Test File bit n & Skip if Clear btfsc f,n 01 11nn nfff ffff Bit Test File bit n & Skip if Set btfss f,n fn <- 0 fn <- 1 pc++ IF fn == 0 pc++ IF fn == aaa aaaa aaaa CALL (jump to) subroutine call aaa TOS <- pc, pc <- aaa fff ffff CLeaR File clrf f f < CLeaR Working register clrw d < CLeaR Watch Dog Timer clrwdt wdt < dfff ffff COMplement File comf f,d d <- f dfff ffff DECrement File decf f,d d <- f dfff ffff DECrement File & Skip on Zero decfsz f,d d <- f--, pc++ IF f == aaa aaaa aaaa GOTO (jump to) aaa goto aaa pc <- aaa dfff ffff INCrement File incf f,d d <- f dfff ffff INCrement File & Skip on Zero incfsz f,d d <- f++, pc++ IF f == LLLL LLLL Inclusive OR Literal to W iorlw LL w <- w + #LL dfff ffff Inclusive OR W to F iorwf f,d d <- w + f dfff ffff MOVe in File (load) movf f,d d <- f LLLL LLLL MOVe Literal into W movlw LL w <- #LL fff ffff MOVe W out to File (store) movwf f f <- w No OPeration nop Do nothing LLLL LLLL RETurn from subroutine with L in W retlw w <- #LL, pc <- TOS RETURN from subroutine return pc <- TOS RETurn From IntErrupt retfie GIE <- 1, pc <- TOS dfff ffff Rotate Left File rlf f,d b7 C 7 file dfff ffff Rotate Right File rrf f,d b0 7 file 0 C Sleep mode on sleep wdt <- 0, Clock off LLLL LLLL SUB W from Literal sublw LL w <- #LL - w dfff ffff SUBtract W from F subwf f,d d <- f - w dfff ffff SWAP File nybbles swapf f,d d <- f[7:4] <--> f[3:0] LLLL LLLL exclusive OR Literal to W xorlw LL w <- w #LL dfff ffff exclusive OR W to F xorwf f,d d <- w f : Flag operates in the normal manner : Not affected a : Address d : Destination; 0=w,1=f f : File register f n : File bit n L : Literal data pc : Program Counter w : Working register wdt : Watch Dog Timer/prescaler TOS : Top Of Stack pc++ : Jump over next instruction == : Equivalent to ++ : Add one -- : Subtract one GIE : Global Interrupt Enable mask # : Constant S.J. Katzen L A T E X2ε Version November 13, 2001 pic_ins14.tex 6/9

7 PIC16F83/84 Special-Purpose Register file summary File Name Power-on All other address Reset Resets Bank 0 00h INDF Uses contents of this to address Data memory (not a physical register) 01h TMR0 8-bit real-time clock/counter XXXX XXXX UUUU UUUU 02h PCL 1 Lower-order 8 bits of the Program Counter h STATUS 1 IRP RP1 RP0 TO PD Z DC C XXX 000??UUU 04h FSR Indirect Data memory address pointer 0 XXXX XXXX UUUU UUUU 05h PORTA RA4 RA3 RA2 RA1 RA0 X XXXX U UUUU 06h PORTB RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0 XXXX XXXX UUUU UUUU 08h EEDATA Data EEPROM Data register XXXX XXXX UUUU UUUU 09h EEADR Data EEPROM Address register XXXX XXXX UUUU UUUU 0Ah PCLATH Write buffer for top 5 PC bits Bh INTCON GIE EEIE T0IE INTE RBIE T0IF INTF RBIF X U Bank 1 80h INDF Uses contents of this to address Data memory (not a physical register) 81h OPTION RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS h PCL 1 Lower-order 8 bits of the Program Counter h STATUS 1 IRP RP1 RP0 TO PD Z DC C XXX 000??UUU 84h FSR Indirect Data memory address pointer 0 XXXX XXXX UUUU UUUU 85h TRISA Port A Direction Register h TRISB Port B Data Direction Register h EECON1 Data EEPROM Data register XXXX XXXX UUUU UUUU 89h EECON2 EEPROM Control register (not a physical register) 8Ah PCLATH Write buffer for top 5 PC bits Bh INTCON GIE EEIE T0IE INTE RBIE T0IF INTF RBIF X U X Not known U Unchanged? Value depends on whether a Watchdog Reset and if in Sleep mode before Reset. Unimplemented; reads as 0. Note 1: Next instruction address if PIC in Sleep mode. S.J. Katzen L A T E X2ε Version November 13, 2001 pic_ins14.tex 7/9

8 Pre-Processor: Standard C #define #undef #include #if #ifdef #ifndef #else #endif #list #nolist #error #pragma Function Qualifiers #inline #separate #int_xxxxx #int_global #int_default Standard C #device #id #fuses CCS C Compiler Version 3 Libraries #use delay #use rs232 #use i2c #use standard_io #use fixed_io #use fast_io Standard C #byte #bit #locate #reserve #rom #zero_ram #asm #endasm Standard C #case #opt #priority _date device pcb pcm pch Standard C: if, else, while, do, switch, case, for, return, goto, break, continue! ~ ,& / % << >> ^ &&?: < <= > >= ==!= = += -+ *= /= %= >>= <<= &= ^= = typedef, static, auto, const, enum, struct, union Arrays up to 5 subscripts Structures and Unions may be nested. Custom bit fields (1-8 bits) within structures. ENUMurated types CONSTant variables, arrays and strings. Full function parameter support (any number). Some support for C++ reference parameters. 8/9

9 Built-in Functions Standard C Char atoi() atol() atoi32() atof() tolower(), toupper() isalnum(), isalpha() isamoung(), isdigit() islower(), isspace() isupper(), isxdigit() strlen(), strcpy() stncpy(), strcopy() strcmp(), stricmp() strncmp(), strcat() strstr(), strchr() strrchr(), strtok() strspn(), strcspn() strpbrk(), strlwr() Delays delay_cycles() delay_us() delay_ms() Capture / Compare / PWM setup_ccpx() set_pwmx_duty() Processor Controls sleep() reset_cpu() restart_cause() disable_interrupts() enable_interrupts() ext_int_edge() read_bank() Standard C Memory memset() memcpy() RS232 I/O getc() putc() gets() puts() printf() kbhit() set_uart_speed() 1C2I/O i2c_start() i2c_stop() i2c_read() i2c_write() i2c_poll() Discrete I/O output_low() output_high() output_float() output_bit() input() output_x() input_x() port_b_pullups() set_tris_x() SPI 2 Wire I/O setup_spi() spi_read() spi_write() spi_data_is_in() Parallel Slave I/O setup_psp() psp_input_full() psp_output_full() psp_overflow() Timers setup_timer_x() set_timerx() get_timerx() setup_counters() setup_wdt() restart_wdt() Standard C Math abs() abs320 acos() asin() atan() ceil() cos() exp() floor() labs() log() logl0() pwr() sin() sqrt() tan() A/D Conversion setup_adc_ports() setup_adc() set_adc_channel() read_adc() Analog Compare setup_comparator() Voltage Ref setup_vref() Internal EEPROM read_eeprom() write_eeprom() read_program_eeprom() write_program_eeprom() read_calibration() Bit Manipulation shift_right() shift_left() rotate_right() rotate_left() bit_clear() bit_set() bit_test() swap() 9/9