Exam 2 E2-1 Fall Name: Exam 2

Transcription

1 Exam 2 E2-1 Fall Short Answer [20 pts] Exam 2 a. [4 points] Show the contents of registers A, B, SP, and X after the following code executes: lds #$a00 ldab #$23 A = ldaa #$87 ldx #$2543 B = pshd pshx SP= pulb pula X= pulx b. [4 points] Calculate the correct checksum for this S-Record: S C6003D c. [4 points] If the SCI is set up for 4800 baud serial communication, what is the width of a single bit? d. [4 points] If two input capture events occur at counts $1033 and $F044, how many counts (in decimal) have occurred between these two events? e. [4 points] For the preceding question assume the answer was 1200 (decimal). If the MCLK is 2 MHz and the prescalar bits PR[2:1:0] are set to 101, how much time transpired between the two input capture events?

2 Exam 2 E2-2 Fall [20 points] Write a function RTI_init() that will initialize the Real Time Interrupt (RTI) subsystem to produce interrupts at a rate one interrupt every milliseconds and enable interrupts. Assume the E-clock is 8MHz. ;********************************************************* ; RTI_init Sets up the RTI subsystem to produce interrupts ; at msecs. Assumes E-clock is 8MHz, enables ; interrupts. ; Input: None ; Output: enables interrupts and stars RTI subsystem RTI_init 3. [20 pts] In this problem, you will write a subroutine called reverse that will print a message in reverse. The string to be printed is pointed to by the X register (address of the first byte of the string is in X). The string is NULL terminated. Your function should print all the characters (except the NULL) in reverse order. For example, if the string contains Testing... your function should print gnitset on the PC screen. You may use any of the basic IO routines

3 Exam 2 E2-3 Fall 2004 we used in lecture and lab (they are provided at the end of the exam). Note: An ASCII table is also included on the last page of the test. Also, your function should not affect any registers or the condition codes (protect them or do not use them). ;********************************************************* ; reverse -- Print the NULL terminated string pointed to ; by X register in reverse order. Does not affect ; any registers or the CCs. ; ; Input: X register points to the string ; Output: ASCII data on the serial port ; (place your code below) $include basicio.asm reverse

4 Exam 2 E2-4 Fall [20 pts] Write a function newrti that will perform the same function as the RTI instruction in the 68HC12 instruction set ( you may not use the RTI instruction itself in your function). Assume the following stacking order on entry to an interrupt: Memory Location SP + 7 SP + 5 SP + 3 SP + 1 SP CPU Register RTN H : RTN L Y H : Y L X H : X L B : A CCR ;******************************************************* ; newrti Function to replace the HC12 RTI instruction ; newrti

5 Exam 2 E2-5 Fall [20 pts] In this problem you will write an improved version of outchar() from the set of standard IO functions we used in the lab. The new improved version will be called newoutchar(). If the SCI is not ready to send a character newoutchar() will not block. Instead, it will save the byte in a special memory location (buffer) and then let an interrupt service routine take care of sending the character when the SCI is ready. The new function still must block if there is already a character queued up in the buffer waiting to be sent, otherwise it would overwrite the waiting character. Put your code in the spaces below. ;************************************************************** ; Name: newoutchar ; Description: outputs ASCII character passed in the A register ; to the SCI serial port without blocking (buffer ; size is one) ;************************************************************** bstatus fcb 00 buffer rmb 1 newoutchar pshc pshb ldab #txdre ; load transmit data register empty mask bitb scisr ; check if ready to transmit beq queueit; set up for isr to handle it if not ready staa scidr ; output ASCII character to SCI exito pulb pulc queueit tst bstatus bne queueit ; block if buffer is full staa buffer ; put the char in the buffer inc bstatus ; mark the buffer full bra exito ; enable SCI transmit interrupts sci_isr ; assume the interrupt vector is correctly mapped ; You should set the SCI to ; disable future sci transmit ; interrupts because you are ; emptying the buffer ; remember to output the ; character in the buffer. ; also, mark the buffer empty ; and be sure the interrupt ; flag is cleared. rti

6 Exam 2 E2-6 Fall 2004 ; Some Basic Character I/O Routines for use in Lab #3 ; Declarations ; Serial Communications Interface (SCI) rxdrf equ 20h ; receive buffer full mask pattern txdre equ 80h ; transmit buffer empty mask pattern scisr equ 00c4h ; SCI control/status register scidr equ 00c7h ; SCI transmit/receive data register ; Name: inchar ; Description: inputs ASCII character from SCI serial port ; and returns it in the A register ; Returns: ASCII character in A register ; Modifies: A register inchar: pshc ci1: ldaa #rxdrf ; load receive data register full mask bita scisr ; check for incoming character beq ci1 ; wait if no character received ldaa scidr ; return ASCII character in A register pulc ; Name: outchar ; Description: outputs ASCII character passed in the A register ; to the SCI serial port outchar: pshc pshb ldab #txdre ; load transmit data register empty mask co1: bitb scisr ; check if ready to transmit beq co1 ; wait if not ready staa scidr ; output ASCII character to SCI pulb pulc ; pmsg -- Print string following call to routine. Note that subroutine ; return address points to string, and is adjusted to point to ; next valid instruction after call as string is printed. pmsg pulx ; Get pointer to string (return addr). ploop ldaa 1,x+ ; Get next character of string. beq pexit ; Exit if ASCII null encountered. jsr outchar ; Print character on terminal screen. bra ploop ; Process next string character. pexit pshx ; Place corrected return address on stack. ; Exit routine. ; Name: getbyte ; Description: inputs two ASCII characters from the HC12 SCI ; and conve them to two hexadecimal digits ; packed into a single byte ; Returns: hex byte equivalent of ASCII characters in A register ; Modifies: A register ; Calls: inchar, outchar, atoh getbyte: pshc jsr inchar ; get first ASCII character jsr outchar ; echo character jsr atoh ; convert ASCII character to hex bcs errhex1 ; if not hex, go to error routine get2: asla asla ; to upper nibble asla asla psha ; shift converted hex digit ; save on stack temporarily jsr inchar ; get second ASCII character jsr outchar ; echo to screen

7 Exam 2 E2-7 Fall 2004 jsr atoh ; convert ASCII character to hex bcs errhex2 ; if not hex, go to error routine oraa 1,sp+ ; OR converted hex digits together pulc errhex1: ldaa #'?' ; get? to prompt for new character jsr outchar bra getbyte errhex2: ldaa #'?' jsr outchar bra get2 ; Name: atoh ; Description: conve an ASCII character to a hexadecimal digit ; Inputs: ASCII character passed via A register ; Returns: converted hexadecimal digit returned in A register, ; CF = 0, result OK; CF = 1, error occured (invalid input) ; Modifies: A register and CC register atoh: pshb pshx pshy suba #30h ; subtract "bias" to get ASCII equivalent blt outhex cmpa #0ah bge cont1 quithx: clc ; return with CF = 0 to indicate result OK puly pulx pulb cont1: suba #07h cmpa #09h blt outhex cmpa #10h blt quithx suba #20h cmpa #09h blt outhex cmpa #10h blt quithx outhex: sec ; set CF <- 1 to indicate error puly pulx pulb ; Name: getword ; Description: get 4 ASCII characters and put into a hex word in the ; D register ; Inputs: 4 ASCII characters typed on the keyboard ; Returns: equivalent hex word in the D register ; Reg. Mod.: D,CC ; Calls: getbyte ; getword: jsr getbyte ; get first byte of the data entered bcs badval ; is there an error in the first byte tfr a,b ; save MSB in B jsr getbyte ; get second byte of data entered bcs badval ; is there an error in the second byte exg a,b ; put MSB in A and LSB in B andcc #$FE ; no errors, clear Z flag badval: orcc #$01 ; error, set Z flag

8 Exam 2 E2-8 Fall 2004 ASCII Table