Method of converting 51 MCU program to AVR

Summarize the conversion from C51 to ICCAVR 

1.
Replace the header files that define registers in C51, such as reg51.h and at89x51.h, with corresponding AVR header files such as io8515.h and io2313.h.

2. Interrupt handling function

In C51, the interrupt keyword is used to indicate that a function is an interrupt handling function. In ICCVAR, the #pragma interrupt_handler preprocessing command can be used to declare it at the beginning of the program. The specific usage is as follows: 
#pragma interrupt_handler
Note that the interrupt and using keywords in the original C51 source program should be deleted. 

3. Processing of bit and sbit data types in C51
ICCAVR does not support bit and sbit data types. Unsigned char can be used to replace these two types. The bit operations are processed using the standard C bit operation function. Online assembly processing can also be adopted. 

4. To initialize the interrupt system timer,
you need to re-assign the corresponding control register according to its function. The method is the same as C51. The details are as follows: the processing of TMOD TCON in MCS51 is changed to the processing of TCCR0 TCCR1A TCCR1B TIFR of AVR. 

The processing of IE IP in MCS51 is changed to
the processing of GIMSK TIMSK MCUCR SREG in AVR. The processing of IE IP in MCS51 is changed to the processing of GIMSK TIMSK MCUCR SREG in AVR. 

5. Change the original C51's handling of the external EEPROM of the watchdog circuit to the handling of the internal EEPROM of the watchdog circuit of the AVR chip. 

6. Change the initialization of MCS51UART to UCR and UBRR and initialized 

7. If an off-chip SRAM is used, the MCUCR should be initialized. If a pin is used as an output pin, its direction register should be initialized. 

8. In principle, the C language in C51 that complies with the ANSI standard does not need to be modified unless it is for the purpose of optimizing the program structure.