Several Issues on Application Programming of C51 Language

The pin diagram and timing diagram of 1549 are shown in Figure 1 and Figure 2 respectively. Assume that DATA OUT is connected to P1.0, CS is connected to P1.1, and CLOCK is connected to P1.2.
Please refer to the relevant information for the specific characteristics of 1549.

Figure 2 TLC1549 timing diagram

Example 2 Calling C language program and assembly language program, the subroutine is as follows:

PUBLIC AD; Entry address
SEG_AD SEGMENT CODE; Program segment
RSEG SEG_AD
USING 0
AD: MOV R6,#00
MOV R7,#00
SETB P1.1
ACALL DELAY
CLR P1.1
ACALL DELAY
MOV R0,#10
RR0: SETB P1.2
NOP
CLR P1.2
DJNZ R0,RR0
ACALL DELAY
MOV 30H,R6; A/D conversion high
; two bits are stored in R6
ACALL CIR
MOV R6,30H
SETB P1.2
NOP
CLR P1.2
MOV 30H,R6
ACALL CIR
MOV R6,30H
MOV R0,#8; A/D conversion low
; 8 bits are stored in R7
RR2: SETB P1.2
NOP
CLR P1.2
MOV 30H,R7
ACALL CIR
MOV R7,30H
DJNZ R0,RR2
RET
CIR: CLR C
MOV C,P1.0
MOV A,30H
RLC A
MOV 30H,A
RET
END [page]

In the above program, the return value of the function is an unsigned integer. According to the calling rules, the high bit of the return value must be in R6 and the low bit in R7, so as to ensure that the data transmission is error-free. In addition, during the calling process, attention must be paid to the stacking of registers. In this way, when A/D conversion is used in the future, the assembly language subroutine AD() can be called in C language.

3 C51 interrupt processing process

The C51 compiler supports the development of interrupt procedures directly in the C source program, thus reducing the tedious work of using assembly language and improving development efficiency. The complete syntax of the interrupt service function is as follows:

void function name (void) [mode]
[reentry] interrupt n [using r]

where n (0~31) represents the interrupt number. The C51 compiler allows 32 interrupts, and the specific interrupt to be used is determined by the 80C51 series chip. r (0-3) represents the rth group of registers. When calling an interrupt function, the register group used by the function called by the interrupt procedure must be the same as that of the interrupt function. "Reentry" is used to indicate whether the interrupt handling function has the "reentry" capability. The C51 compiler and its extension of the C language allow programmers to control all aspects of interrupts and use register groups. This support enables programmers to create efficient interrupt service programs. Users only need to care about interrupts and necessary register group switching operations in the C language.

Example 3 Assume that the FOSC of the microcontroller is 12MHz, and it is required to program using T0 mode 1 to output a square wave with a period of 2ms at the P1.0 pin.

The interrupt service program written in C language is as follows:

#include
sbit P1_0=P1^0;
void timer0(void)interrupt 1 using 1 {
/*T0 interrupt service program entry*/
P1_0=!P1_0;
TH0=-(1000/256); /*Reload the initial count value*/
TL0=-(1000%256);
}
void main(void)
{
TMOD=0x01; /*T0 works in timer mode 1*/
P1_0=0;
TH0=-(1000/256); /*Preset the initial count value*/
TL0=-(1000%256);
EA=1; /*CPU turns on interrupt*/
ET0=1; /*T0 turns on interrupt*/
TR0=1; /*Start T0*/
do{}while(1);
}

When writing interrupt service routines, it is important to note that parameters cannot be passed and there cannot be return values.

4 Conclusion

C51 compiler can not only shorten the development cycle of single-chip control systems, but also facilitate debugging and maintenance. In addition, C51 language has many powerful functions, such as providing rich library functions for users to call directly, complete compilation control instructions to provide necessary symbol information for program debugging, etc. In short, C51 language is a powerful tool for a large number of single-chip developers.