Motorola 68HC12 Manual de usuario

ECSE-4790 Microprocessor Systems Design

Motorola 68HC12 User's Manual

Lee Rosenberg

Electrical and Computer Systems Engineering

Rensselaer Polytechnic Institute

Revision 1.1

8/10/00

Table of Contents: page

1. Introduction 2

2. Basic Programming notes for the 68HC12 3

3. D-Bug 12 Monitor Program 4

4. 68HC12 Hardware 7

a) Ports 7

b) A/D Converter 8

c) Timer Functions 12

i) Timer Output Compare 13

ii) Output Compare 7 14

iii) Timer Compare Force Register 15

iv) Input Capture 15

5. Interrupt Service Routines 16

a) Overview 16

b) Interrupt Priority 17

c) Real Time Interrupt 18

d) Timer Overflow Interrupt 19

e) Pulse Accumulator Edge Triggered Interrupt 20

f) Pulse Accumulator Overflow Triggered Interrupt 22

g) Output Compare Interrupt 23

h) Input Capture Interrupt 24

i) A/D Converter Interrupt 25

j) IRQ Interrupt 26

k) Port H Key Wakeup Interrupt 27

l) Port J Key Wakeup Interrupt 28

1. Introduction:

The Motorola 68HC12 is a 16-bit microprocessor descended from the 68HC11. The

design has a number of major improvements over the 6811 and several new features

that are not found on the 6811. The biggest change is the expansion from an 8-bit

bus to a full 16-bit bus for both the data and address. Other improvements include

an increase in the number of A/D converter registers, Timer output compare and

input capture pins, and I/O ports. Also added is a second SCI connector and a new

interrupt, called a Key Wakeup interrupt.

This manual is intended to provide a brief introduction to the 68HC12 and how to

program it in C using the Introl C compiler 4.00. This manual is intended

primarily for those people who are already familiar with the Motorola 68HC11. This

manual also assumes that the reader has basic familiarity with the C programming

language.

2. Basic Programming Notes:

There are 3 header files that must be included with any code written for the 68HC12

using the Introl C compiler. These are:

HC812A4.H - This file contains all the register declarations for the 6812.

INTROL.H - This file contains several function declarations needed by Introl to

compile the program.

DBUG12.H - This contains the information need to call the D-Bug12 routines and to

handle interrupts. Omitting this file will result in the calls to the D-Bug12

routines being flagged as errors by the compiler.

Your main function must be of the format: void _ _main(). The two (2) underscores

before main are necessary, as that is the format that Introl uses to recognize the

main function of the program.

3. D-Bug12:

D-Bug12 is the monitor program for the 6812 EVB. This is similar to the BUFFALO

monitor used on the 6811. Unlike the BUFFALO monitor, the D-Bug12 monitor is a

series of C functions that are stored in an EPROM on the EVB. These functions can

be called by the user to handle both I/O and several of the common C language ANSI

functions.

All calls to the D-Bug12 routines follow the same format. The format is:

DB12->"routine name";

The "DB12->" is used as a cast pointer that allows the compiler to reference the

EPROM for the different routines. The routine name is just the name of the routine

and any parameters that are being passed to the function. If the function returns

a value to the program the return value can be assigned to a variable. This is

done as follows:

temp=DB12->"routine name";

This assigns the return value of the routine to a variable named temp.

As always the variable must be declared in the program.

It is important to note that if you do not include the "DB12->" with the function

call the compiler will return an error message. The error message that is returned

is that the function does not exist. Putting the "DB12->" before the function name

will solve this problem.

D-Bug12 Functions

Readers interested in a more in-depth explanation of the D-Bug12 routines are

referred to Motorola Document an1280a, "Using the Callable Routines in D-Bug 12"

(available on the web at http://www.ecse.rpi.edu/Courses/CStudio/appnotes/).

getchar

This function will get a single character of input from the user.

Function Prototype: int getchar(void);

Return Value: This returns the character from the keyboard in

hexadecimal ASCII.

printf

This will display a string of characters to the screen.

Function Prototype: int printf(char *s);

Return value: The number of characters that were transmitted.

NOTE: The Introl 4.0 compiler has an error in this function. The first parameter in

the list is not printed properly. There are workarounds for some cases that are

given in examples in class handouts. In any case, simple strings without variables

will work without problems.

To display a variable, the variable is represented using %y in the printf

statement, where y is chosen from the table below to match the variable type. To

display a signed decimal integer stored in a variable num, the function call would

look like:

DB12->printf("This is the value of num: %d", num);

d, i

int, signed decimal number

int, unsigned octal number

int, unsigned hexadecimal number using a-f for 10-15

int, unsigned hexadecimal number using A-F for 10-15

int, unsigned decimal

int, single character

char *, display from a string until '\0'

void *, pointer

putchar

This will display a single ASCII character on the screen.

Function Prototype: int putchar(int);

Return Value: The character that was displayed.

GetCmdLine

This function is used to read in a line of data from the user and store it in an

array. Each character that is entered is echoed back to the screen using a call to

the putchar function. Only printable ASCII characters are accepted by the function

with the exception of carriage return and backspace.

Function Prototype: int GetCmdLine(char *CmdLineStr, int CmdLineLen);

Return Value: An error code of NoErr.

The location where data that is read in is stored and the number of characters that

are to be read, are determined by CmdLineStr and CmdLineLen respectively.

CmdLineStr is a char array that is created by the programmer. This is where the

input line from the user is stored.

CmdLineLen is the length of the string to be read in. A total of CmdLineLen -1

characters may be entered by the user before the GetCmdLine function exits. The

user may also use a carriage return to exit before the value of CmdLineLen has been

reached.

Backspace may be used to delete unwanted characters from the line that the user

entered. The character will be erased from the screen and the memory array.

isxdigit

This routine determines if c is a member of the set 0..9, a..z and A…Z

Function prototype: int isxdigit(int c);

Return Value: If c is part of the set the function returns

true (1), if c is not a part of the set the function

returns a false (0).

toupper

This routine is used to convert lower case letters to upper case letters.

Function Prototype: int toupper(int c);

Return Value: The uppercase value of c. If c is already an

uppercase letter it returns c.

isalpha

This routine determines if c is a member of the set a…z and A…Z

Function Prototype: int isalpha(int c);

Return Value: If c is part of the set it returns true (1), if it

is not a part of the set it returns a false (0).

strlen

This routine determines the length of the string that is passed in as a parameter.

The string must be null terminated.

Function Prototype: unsigned int strlen(const char *cs);

Return Value: The length of the string pointed to by cs.

strcpy

This routine makes a copy of string two to string one. The string to be copied

must be null terminated.

Function Prototype: char* strcpy(char *s1, char *s2);

Return Value: A pointer to s1.

out2hex

This outputs an 8-bit number on the screen as two hexadecimal numbers.

Function Prototype: void out2hex(unsigned int num);

Return Value: None

out4hex

This outputs a 16-bit number on the screen as four hexadecimal numbers.

Function Prototype: void out4hex(unsigned int num);

Return Value: None

SetUserVector

This routine is used for handling Interrupt Service Routines and will be described

in the section on interrupts.

Notes:

The printf, putchar, out2hex, and out4hex routines do not generate carriage returns

or line feeds when they are called. To do this you must include \n\r in either a

putchar or a printf statement.

4. 68HC12 Hardware:

This section explains the operation of the hardware on the 68HC12. It includes the

I/O ports, the A/D converter and the timer functions. Hardware interrupts are

explained in the next section. For more information on this material, refer to

Motorola document MC68HC812A4TS/D, "Motorola 68HC12 Technical Summary".

Ports:

All port names are of the format _H12PORTx, where x is the capital letter of the

port you are trying to access. i.e. Port A is _H12PORTA.

Ports A and B are used as the address bus for the 68HC12. They are not usable as

I/O by the programmer. Port A is the high order byte and port B is the low order

byte.

Ports C and D are used as the data bus for the 68HC12. They are not usable for I/O

by the programmer. Port C is the high order byte and port D is the low order byte.

Port E is used to generate control signals needed to access the external memory.

As a result the programmer can not use it for I/O. Port E pin 1 is used as the

input for the IRQ and Port E pin 0 is used as the input for the XIRQ.

Port F is used to control chip selects for the external memory and other chips. The

programmer can not use it as I/O.

Port G is a 6-bit general purpose I/O port. The direction of the port is controlled

by _H12DDRG. When an _H12DDRG bit is set to 0, the port pin is an input and when

it is set to 1 it is an output.

Port H is an 8-bit general purpose I/O port. The direction of the port is

controlled by the _H12DDRH. When _H12DDRH bit is set to 0, the port pin is an

input and when it is set to 1 it is an output.

Port J is an 8-bit general purpose I/O port. The direction of the port is

controlled by the _H12DDRJ. When _H12DDRJ bit is set to 0, the port pin is an

input and when it is set to 1 it is an output.

Port S is used for the SCI and the SPI. It can also be used for general I/O if the

SCI or SPI are not being used. Bits 0 and 1 are SCI0. These are used as the

interface to the terminal and can not be used as I/O. Bits 2 and 3 are SCI1 and

bits 4-7 are the SPI. These can be used as general I/O if SCI1 and the SPI are not

being used. The direction of the port is controlled by _H12DDRS.

Port T is used for the timer interrupts and the pulse accumulator. If the

interrupts are not being used then Port T can be used for general I/O. The port

direction is controlled by _H12DDRTT. Note: The two T's are not a typo.

Port AD is used exclusively as the input to the A to D converter. It can not be

used for any other I/O.

Ports G, H, and Port E pin 0 have optional pull-up resistors inside. These are

controlled by the _H12PUCR register. To enable the pull-up resistor for Port H

write a one to bit 7, for Port G write a one to bit 6, for Port E write a one to

bit 4 of _H12PUCR. To disable the pull-up resistors to a particular port, write a

0 to the appropriate bit.

A to D Converter:

This section covers the basic function of the A/D converter. The A/D converter

uses a dedicated port, port AD, for its inputs. There are 8 A/D converter channels

on the HC12 and, unlike the 6811, there are also 8 A/D registers allowing 8

simultaneous readings. The implementation of the A/D converter allows for two

different methods of operating the A/D converter. This section covers the polling

method. The interrupt based operation is explained in the section on interrupts.

The A/D converter conversion sequence consists of either 4 or 8 conversions and can

convert either one channel or multiple channels. In scan mode operation, polling

based operation, the flag is set after the conversions have been completed,

signaling the completion of the A/D cycle.

Before running the A/D converter, the system must be initialized by the user.

There are 4 registers that are used to control the A/D Converter. These are

_H12ADTCTL2, _H12ADTCTL3, _H12ADTCTL4, and _H12ADTCTL5.

_H12ADTCTL2 contains several of the A/D Converter enable bits. Bit 7 is the A/D

power up (ADPU). When this is set to one the A/D converter is enabled, when it is

zero then the A/D converter is disabled. Bit 1 is the A/D converter interrupt

enable (ASCIE). The interrupt is enabled when the bit equals one and disabled when

the bit is set to zero. In scan mode this bit is set to 0, to disable interrupts.

Bit 0 is the interrupt flag (ASCIF) which is not used in the polling version of the

A/D converter.

_H12ADTCTL2:

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

ADPU

AFFC

AWAI

unused

ASCIE

ASCIF

_H12ADTCTL3 should always be set to 0x00. This is used to control several actions

that are related to how the A/D converter operates in background debug mode. As

the D-Bug12 monitor is being used, the background debug mode is not being used and

these features should be disabled.

_H12ADTCTL4 is used to select the sample time of the A/D converter and to set the

prescalar for the clock.

_H12ADTCTL4:

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

unused

SMP1

SMP0

PRS4

PRS3

PRS2

PRS1

PRS0

There are four different sample times available for the A/D converter. The sample

time is selected by setting the value of SMP1 and SMP0. The different sample times

that can be used are listed in table 1.

Table 1: Sample Times

SMP1 SMP0 Sample Time________

0 0 2 A/D clock periods

0 1 4 A/D clock periods

1 0 8 A/D clock periods

1 1 16 A/D clock periods

The prescalar that is used by the A/D converter is determined by the value of PRS0-

PRS4. The clock input to the prescalar is an 8 MHz clock. This allows for an A/D

conversion frequency of 500 kHz to 2 MHz. The different prescalar values are

listed in Table 2.

Table 2: Prescalar Values

Prescale Value Divisor___

00000 Do not use

00001 /4

00010 /6

00011 /8

00100 /10

00101 /12

00110 /14

00111 /16

01xxx Do not use

1xxxx Do not use

_H12ADTCTL5 is used to select the conversion mode, which channels are to be

converted and to initiate the conversions. The conversion sequence is started by

any write made to this register. If a write is made to this register while a

conversion sequence is in progress, the conversion is aborted and the SCF and CCF

flags are reset.

_H12ADTCTL5:

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

unused

S8CM

SCAN

MULT

S8CM is used to select between making 4 conversions, when the bit is set to zero,

and 8 conversions, when the bit is set to one.

SCAN is used to select between performing either a single conversion or multiple

conversions. If SCAN is set to zero, then a single conversion will be run and the

flag will then be set. If SCAN is set to 1, then the A/D converter will run

continuous conversions on the A/D channels.

MULT determines whether the conversion is run on a single channel or on multiple

channels. When MULT zero, the A/D converter runs all the conversions on a single

channel, which is selected by CD,CC,CB, and CA. When MULT is one, the conversion

is run on several different channels in the group specified by CD,CC,CB, and CA.

The possible channel combinations are in Table 3.

Table 3: A/D Converter Settings

S8CM CD CC CB CA Channel Signal Result in ADRx if MULT = 1

0 0 0 0* 0* AN0 ADR0

0 0 0 0* 1* AN1 ADR1

0 0 0 1* 0* AN2 ADR2

0 0 0 1* 1* AN3 ADR3

0 0 1 0* 0* AN4 ADR0

0 0 1 0* 1* AN5 ADR1

0 0 1 1* 0* AN6 ADR2

0 0 1 1* 1* AN7 ADR3

0 1 0 0* 0* Reserved ADR0

0 1 0 0* 1* Reserved ADR1

0 1 0 1* 0* Reserved ADR2

0 1 0 1* 1* Reserved ADR3

0 1 1 0* 0* V RH ADR0

0 1 1 0* 1* V RL ADR1

0 1 1 1* 0* (V RH + V RL )/2 ADR2

0 1 1 1* 1* TEST/Reserved ADR3

1 0 0* 0* 0* AN0 ADR0

1 0 0* 0* 1* AN1 ADR1

1 0 0* 1* 0* AN2 ADR2

1 0 0* 1* 1* AN3 ADR3

1 0 1* 0* 0* AN4 ADR4

1 0 1* 0* 1* AN5 ADR5

1 0 1* 1* 0* AN6 ADR6

1 0 1* 1* 1* AN7 ADR7

1 1 0* 0* 0* Reserved ADR0

1 1 0* 0* 1* Reserved ADR1

1 1 0* 1* 0* Reserved ADR2

1 1 0* 1* 1* Reserved ADR3

1 1 1* 0* 0* V RH ADR4

1 1 1* 0* 1* V RL ADR5

1 1 1* 1* 0* (V RH + V RL )/2 ADR6

1 1 1* 1* 1* TEST/Reserved ADR7

Stared (*) bits are “don’t care” if MULT = 1 and the entire block of four or eight

channels make up a conversion sequence. When MULT = 0, all four bits (CD, CC, CB,

and CA) must be specified and a conversion sequence consists of four or eight

consecutive conversions of the single specified channel.

_H12ADSTAT is used to determine the status of the conversion process. Unlike most

of the registers in the HC12 this is a 16-bit register. The Sequence Complete Flag

(SCF) is used to signal the completion of the conversion cycle. When SCAN = 0, the

setting of the SCF signals the completion of the cycle, when SCAN = 1, it signals

the completion of the first conversion cycle.

_H12ADSTAT:

bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8

SCF

unused

CC2

CC1

CC0

CCF7

CCF6

CCF5

CCF4

CCF3

CCF2

CCF1

CCF0

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

CC2-CC0 are the conversion counter. They are the pointer for the conversion cycle

and reflect which result register will be written to next.

CCF7-CCF0 are the Conversion Complete Flags (CCF) for the individual A/D channels.

When the conversion sequence for a channel has been complete the flag is set. The

flags can be cleared by reading the A/D register for the channel and by reading the

_H12STAT register.

The results of the A/D conversions are stored in the A/D converter result

registers. These registers are called _H12ADR0H through _H12ADR7H. When

converting multiple channels, the destination register used to store the results of

each channel that is converted is listed in Table 3. When converting a single

channel, the results are in _H12ADR0H - _H12ADR3H for a 4 conversion sequence and

_H12ADR0H - _H12ADR7H for an eight conversion sequence.

Sample Code

This code turns on the A/D converter while disabling the A/D interrupt. It then

performs 4 conversions on channel 0 of the A/D converter and displays the result

that is stored in the result registers to the screen.

_H12ADTCTL2=0x80; // turn on ATD and off the interrupt

_H12ADTCTL3=0x00; // don't stop at breakpoints

_H12ADTCTL4=0x43; // Set prescalar (/8) & sample time 8 periods

_H12ADTCTL5=0x00; // check AN0, 4 conversions and stop

while(!(_H12ADTSTAT & 0x8000)); // wait for flag to be set

DB12->out2hex(_H12ADR0H); // Display A/D result registers

DB12->printf("\n\r");

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