Anywhere, I do the experimental board by using circuit of the basic Microcontroller in order to carry out this content. Generally, in the side of programming with Microcontroller, I will mention the part of programming to connect Serial Port, but there will be programming to control Timer also. Why use Timer? Because we will create Baud Rate, after that we will go to programming to get and send data through Serial Port of Microcontroller

Managing to Timer’s working

TCON (Time Control Register) and TMOD (Time Mode Register) 

We take the both to do for controlling Timer’s working in order to use as looping to measure time taken of Baud Rate, is to set value in TMOD such as TMOD=00100000B.  Here, we use getting and sending data 11 bit, will have 8 data bit, Start bit, Stop bit, Custom data bit. All we will set Timer to occur interrupt that we will set at IE (Interrupt Enable Register), setting to be zero every bit, for Baud rate of getting and sending data, will use the rate of Timer Overflow together with the value of SMOD(Serial Mode Register). For the value that will set for Timer in order to create the rate of getting and sending of Serial Port in Microcontroller can use the below table.

The table of setting value for Timer in order to use for Baud Rate

Frequency(MHz)	Baud Rate of Serial Port(bit/sec)	The value of Timer that will be set
11.059	1200	E8H
11.059	2400	F4H
11.059	4800	FAH
11.059	9600	FDH

     Programming for setting value of working of Timer

We may conclude programming for setting of Timer such as Baud Rate of Serial port=9600 bit/sec 

MOV TMOD,#00100000B  ; setting value in TMOD Register to begin the new value automatically.    

MOV IE,#00000000B   ; setting value not Timer Interrupt

MOV TL1,#FDH          ;setting Baud Rate 9600 bit/sec

MOV TH1,#FDH        

SETB TR1                   ; command Timer 1 to work

Programming to connect with Serial Port 

Serial Port Control Register named SCON

Doing as controller of process of getting and sending of Serial Port in Microcontroller that will be what mode for getting data and sending data. This SCON, will manage, but we have to set the function to SCON before like the details in the following,

The table of showing the component of SCON

The positions of Bit	Names	Functions
0	RI	Interrupt in sending data
1	TI	Interrupt in getting data
2	TR8	Getting data if use Mode 2,3 will be Bit No. 9
3	TB8	Sending data if use Mode 2,3 will be Bit No. 9
4	REN	Setting to get data or not
5	SM2	If use connect two more Microcontroller
6	SM1	Choose Mode of parallel port
7	SM0	Choose Mode of parallel port

Serial Port Buffer Register named SBUF 

It is keeper of data for getting or sending data through Serial Port in Microcontroller. If we will write program to get data, we have to move data in Buffer to use.

Such as MOV A, SBUF, etc.

If we will send data out to Serial Port in Microcontroller, we have to move data to Buffer the same. 

Such as MOV SBUF,A or MOV SBUF,#31H, etc.

 Programming to get data

 JNB RI,$            ; compare condition until be real when Buffer Receive already.

CLR RI               ; clear value of RI(Receive Interrupt) bit in SCON Register 

MOV A,SBUF  ; keep value from Buffer to keep in Register A

Programming to send data

MOV SBUF,#43H  ; get ค่าแอสกี้=43H to keep at Buffer in sending data through Serial Port

JNB TI,$              ;  compare condition as real when Buffer Send alreay

CLR TI                ; clear value of TI(Transmit Interrupt) bit in SCON Register

From the content I mention above, I think we may understand and can use to program to connect Serial Port of Microcontroller by yourself. For more understanding, I have the project about this content.

Microcontroller connecting with PC as RS-232 through Serial Port

The learning outcome of this article

1) To be the fundamental in programming for controlling the Microcontroller Serial Port’s working.

2) To know Register for controlling Timer and Serial Port.

3) Can apply program Microcontroller connecting with program on PC through Serial Port

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1.      Operation Code consists of 2-4 alphabets such as MOV, SJMP, etc.

2.      Operand is operated; it will be the set of alphabets that notify operation that will be one set or 2 sets. If there will be 2, it will have comma (,) like A, #20H, etc.

3.      Comment is explanation the meaning of codes that will be preceded by semicolon (;).

The group of commands of mnemonic code, are divided into 4 main groups,

1.      Logic, such as AND,OR,XOR,NOT

2.      Mathematic  such as INC,DEC,ADD,SUBB,MUL,DIV

3.      Control to manage working

4.      Processing as Boolean

The table of writing command doing with data
How to do with data	Examples
1. Directly do at memory position 2. Indirectly do at register position 3. Directly give value with memory 4. According to value of Register 5. According to arrangement 6. Do according condition	MOV A,8CH MOV A,@R1 MOV A,#7FH MOV A,R7 MOVC A,@A+PC INC DPTR

The table of the basic command of Assembly
Commands	Examples	Meanings
MOV	MOV A,R1 MOV A,14H MOV A,#7FH MOV P1,A	Using for transferring data from start to terminal. there will be P1 is using to send value out at Output leg of microcontroller such as 8051,Z80
ADD	ADD A,R1 ADD A,14H ADD P1,A	Using for adding data that will have A on the left, if Add R1, A <—- X wrong.
ANL	ANL A,R1	Is to And value, then keep at the terminal. <– This is doing And value in A with R1, then keeps value in A as usual.
CJNE	CJNE A,#02H,OUT MOV P1,#01H END	Is to do comparison, if the value isn’t be equal, it will skip working <– such as value A isn’t be equal with 02, it will skip at the line named OUT, if to be equal, will take value at P1.
OUT	OUT DX,AL	For sending to PC Port
CLR	CLR A	For clearing data as zero <– A=0
INC	INC R1	Increasing value –> R1=R1+1
DEC	DEC R1	Decreasing value –> R1=R1-1
JNZ	ADD P1,A	Skipping to other Label, if A(Accumulator) isn’t be zero
ROR	ROR AL,1	Moving data bit to the right, 1 bit 1 time 1=0001—>1000
ROL	ROL AL,1	Moving data bit to the left, 1 bit 1 time 1=0001—>0010
LOOP	LOOP 0123	For looping working at Address 0123
INT20	INT 20	Show output on screen.
INT21	INT 21	Getting value from keyboard.

Programming to control Card I/O 8255 port in Debug

1. Type the word, Debug at C:\ then will get – on the below line.
      2. then, type a, that will get data.
      3. Type Code like this,

4. Press Enter 1 time, then type P or R, you will get for running program that continuously Enter, it will have result like this,

      From the method I mentioned is experiment to easily program, but writing for real using, you have to write Editor so that you can keep and edit in the next time.

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The command used to control I/O Printer Data Port
send signal out Printer Port, we use the form of command like this,

OUT Address data port, Value
Address data port of printer=0378
Value that will send to printer data port, the number that control 8 bit is 00-FF.

OUT DX,AL

(more…)

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Although, there is no language, it can be programmed to directly connect along port. So, you have to use the function from DLL file for sending the function that send and read value from port of Pascal like the following, (more…)

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1. New project Microsoft VC++ 6 (more…)

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The context is the fundamental of programming principle by MS Visual C++ 6 connecting through Serial Port of the computer in sending and getting alphabet. For the form of how to programming that will not have ready-made control that will be used like Visual Basic. In this section, you have to use programming principle as reading and writing data file. Anyhow, the data that will be got and sent out to port is like reading and writing data on file. I prepare the step for understanding in programming like this,

4 steps for connecting Serial Port

1. Set variable for keeping file names, data read (Buffer),file handles, value of getting and sending data.

HANDLE hComm; // handle for COM port
DCB dcb; // data structure that keep value for connecting serial port
char * chCommPort = “COM1″; // we use com port 1
int valReturn; // keep returning value back in some function.
char chBuffer; // keep alphabet in getting and sending data.
unsigned long nReadPort; //keep returning value back in function, ReadFile
unsigned long nWrittenPort; // keep returning value back in function, WriteFile (more…)

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First of all, I want to disclaim that I don’t use Borland C++ Builder in programming because I practice just MS VC++ 6 , but trying to search information in the internet , then I find the answer that we have to use in writing function to connect to I/O Port by helping of assembly. I reminded that I used the method of writing in Delphi that you will use it to write within your program or will write as function in binary file. It will be more convenient in using that has how to write like the following, (more…)

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Programming Microsoft Visual C++ 6 communicating Parallel Port

Outp(port,bytedata)	Send value out port as byte
Outpw(port,worddata)	Send value out port as word	Such as Outp(0×378,0xF1)
Outpd(port,worddata)	Send value out port as byte double words.
inp(port)	Read value as byte from port
inpw(port)	Read value as word from port.	Such as inpw(0×378)
inpd(port)	Read value as double words from port.

You can notice that the structure of function is like programming by VB because Dll File that is used in VB that is written from C. I will not mention the fundamental of communicating port. (more…)

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In this program, we will use file conio.h that is include file for using function _outp() and _inp()

In this section, I will do as explanation with pictures (Visual Learning), controlling with messages and the arrange of number shown because if you write explanation as the last contexts, you will be hard to understand. (more…)

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From the part 1, I mentioned about communication as interrupt. In this part, I will present you about communication as polling. The working like this, the flow of data will not be smooth. CPU cannot anticipate that when the new data arrive. It will verify the time with getting and sending data by speed rate that is higher than speed rate that send through keyboard. (more…)

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