MICROPORTS.H
Information in the microports.h file would contain bit definitions for the configuration registers and I/O ports. Microcontroller suppliers provide most of this information and in many cases they might even supply a predefined header file for use with the microcontroller. In the example, PORT A is an 8-bit port with bits defined Pax, where x is the bit number from 0 to 7, and a configuration data direction register (DDR) bits DDAx. BITx is defined in a top-level header file where all of the bits in the data type are set to zero except for the x^th bit.

// I/O PORT A REGISTER
#define PA7    BIT7
#define PA6    BIT6
#define PA5    BIT5
#define PA4    BIT4
#define PA3    BIT3
#define PA2    BIT2
#define PA1    BIT1
#define PA0    BIT0

// I/O PORT A DATA DIRECTION REGISTER
#define DDA7    BIT7
#define DDA6    BIT6
#define DDA5    BIT5
#define DDA4    BIT4
#define DDA3    BIT3
#define DDA2    BIT2
#define DDA1    BIT1
#define DDA0    BIT0

The following is a truncated structure definition for the ports in a microcontroller. U8 stands for unsigned data type 8-bits long and is a reassignment of the standard C type defined in the COMPILER.H file.

typedef  struct {
         volatile   U8 PORTA;        // port A
         volatile   U8 PORTB;        // port B
         volatile   U8 DDRA;        // data direction port A
         volatile   U8 DDRB;        // data direction port B
         volatile   U8 Reserved1;
         volatile   U8 Reserved2;
         volatile   U8 Reserved3;
         volatile   U8 Reserved4;
         volatile   U8 PORTE;        // port E
         volatile   U8 DDRE;         // data direction port E
         volatile   U8 PEAR;         // port E assignment register
         volatile   U8 MODE;         // mode register
         volatile   U8 PUCR;         // pull-up control register
         volatile   U8 RDRIV;        // reduced drive of I/O lines
         volatile   U8 Reserved8;
         volatile   U8 Reserved9;
                    .    .    .
                    .    .    .
                    .    .    .
               } D60Regs_t;

VECTORS
A separate file would define the interrupt subroutine vector table. In the following example, the isr_00 label jumps to a routine that has, as its only function, a return from subroutine. The isr_00 label is included at every location in the vector table that doesn't have an associated interrupt subroutine. If for some reason, an interrupt occurs on a channel that is not defined, function is immediately returned to the main processing. The microcontroller supplier usually provides a template of this file.

// INTERRUPT VECTOR TABLE: LOCATED AT $FFC2 // - $FFFF FOR HC12d60 
const _vectab[]=
{
    isr_00,
// CGM lock and limp home
     CAN_transmit_isr,
// MSCAN tranmit
     CAN_receive_isr,
// MSCAN receive
     CAN_error_isr, 
// MSCAN errors
     isr_00,
// Pulse Accumulator B overflow
     isr_00,
// Modulus down counter underflow
     isr_00,
// Key wake-up G or H
     CAN_wakeup_isr,
// MSCAN wake-up
     isr_00,
// ATD 0 or 1 interrupt
     isr_00,
// SCI 1 interrupt
     isr_00,
// SCI 0 interrupt
     isr_00,
// SPI complete
     isr_00,
// Pulse accumulator input
     isr_00,
// Pulse accumulator overflow
     isr_00,
// Timer overflow interrupt
     isr_00,
// Timer channel 7 interrupt
     ISR_THREE,
// Timer channel 6 interrupt USED FOR MAIN // LOOP CLOCK
     isr_00,
// Timer channel 5 interrupt
     isr_00,
// Timer channel 4 interrupt
     isr_00,
// Timer channel 3 interrupt
     isr_00,
// Timer channel 2 interrupt
     isr_00,
// Timer channel 1 interrupt
     ISR_TWO,
// Timer channel 0 interrupt 2ms BACKGROUND // LOOP CLOCK
     isr_00,
// Real time interrupt
     ISR_ONE,
// INTCR IRQ
     isr_00,
// External interrupt request
     isr_00,
// Software interrupt
     isr_00,
// Unimplemented Instruction Trap
     isr_00,
// COP failure reset
     isr_00,
// Clock monitor fail reset
     _stext,
// reset }

The rest of the ECU_HSIS.H would define the hardware to software interface. This file contains the following components:

1. The microcontroller's memory map.

2. System clock frequency defines.

3. Microcontroller peripheral definitions.

MICROCONTROLLER MEMORY MAP
Define the microcontrollers memory map upfront. This will help to quickly redefine the memory map when changing microcontrollers.

#define START_OF_REG_RAM       (0x0800)
#define LENGTH_OF_REG_RAM      (512)

// Register bytes
#define START_OF_BASE_RAM      (0x0000)
#define LENGTH_OF_BASE_RAM     (2048)

// RAM bytes 
#define START_OF_EEPROM        (0x0c00)
#define LENGTH_OF_EEPROM       (1024)

// EEprom bytes 
#define END_OF_EEPROM          (START_OF_EEPROM+LENGTH_OF_EEPROM-1) 
#define START_OF_ROM           (0x1000)
#define START_OF_VECTOR_TABLE  (0xFF00)

// ISR vector table 
#define LENGTH_OF_VECTOR_TABLE (0xFF)