RS232-Fragen

Hi,

ich möchte zwei AtMega per RS232 kommunizieren lassen.

1. Frage: Woher weiß der Bascom Terminal Emulator, dass ich im Programm "Dim Eingabe as String * 8" eingegeben habe und ich folglich im Emulator nur 8 Zeichen eingeben kann?

2. Frage Unabhängig von der Anzahl der vom PC gesendeten Zeichen wartet das Programm aus der Bascomhilfe (s.u) von der Eingabe des ersten Zeichens bis zum abschließenden Return. (Programm stoppt solange). Warum, also woher weiß das Programm, dass ich mit der Eingabe angefangen habe?

Code:

---


'-----------------------------------------------------------------------------------------

'name                    : rs232buffer.bas

'copyright                : (c) 1995-2005, MCS Electronics

'purpose                  : example shows the difference between normal and buffered

'                          serial INPUT

'micro                    : Mega161

'suited for demo          : yes

'commercial addon needed  : no

'-----------------------------------------------------------------------------------------

 

$regfile = "m161def.dat"                                  ' specify the used micro

$crystal = 4000000                                        ' used crystal frequency

$baud = 9600                                              ' use baud rate

$hwstack = 32                                              ' default use 32 for the hardware stack

$swstack = 10                                              ' default use 10 for the SW stack

$framesize = 40                                            ' default use 40 for the frame space

 

'first compile and run this program with the line below remarked

Config Serialin = Buffered , Size = 20

 

 

Dim Na As String * 10

 

'the enabling of interrupts is not needed for the normal serial mode

'So the line below must be remarked to for the first test

Enable Interrupts

 

Print "Start"

Do

  'get a char from the UART

 

  If Ischarwaiting() = 1 Then                            'was there a char?

    Input Na   

    Print Na                                          'print it

  End If

 

  Wait 1                                                  'wait 1 second

Loop

 

'You will see that when you slowly enter characters in the terminal emulator

'they will be received/displayed.

'When you enter them fast you will see that you loose some chars

 

'NOW remove the remarks from line 11 and 18

'and compile and program and run again

'This time the chars are received by an interrupt routine and are

'stored in a buffer. This way you will not loose characters providing that

'you empty the buffer

'So when you fast type abcdefg, they will be printed after each other with the

'1 second delay

 

'Using the CONFIG SERIAL=BUFFERED, SIZE = 10 for example will

'use some SRAM memory

'The following internal variables will be generated :

'_Rs_head_ptr0  BYTE , a pointer to the location of the start of the buffer

'_Rs_tail_ptr0  BYTE , a pointer to the location of tail of the buffer

'_RS232INBUF0 BYTE ARRAY , the actual buffer with the size of SIZE

---

zu 2. Das Terminal sendet bei jedem Tastendruck den ASCII-Wert des Zeichens, das dem Tastendruck entspricht als Byte.
Dieses landet im UDR-Register des AVR und gleichzeitig wird ein Flag gesetzt, das URXC C steht für complete, also Zeichen ganz empfangen.
Das ischarwaiting fragt dieses Flag ab und geht dann in die input Routine.
Input wartet immer auf ein CR also die Enter Taste ASCII=13, solange dies nicht kommt werden die ankommenden Zeichen einfach aneinander gereiht.