This lesson will show how simple a tiny class 2 scanner can be. For this purpose, we will use message filtering to view only the functional messages from module $60. As before, the code will be broken into sections and discussed in detail. First we need to set up the handler and set the filtering options. We set our module ID to $F0, but this is not necessary for filtering functional messages, because those only contain a source ID, not a target ID. For physical messages we would be able to discriminate the target ID also.
ORG 050H buffer: DS 16 MAIN: LCALL CLS ;clear the screen MOV DPTR,#buffer ;as before, pass the buffer and length to the OS MOV A,#16 LCALL DLC_INIT ;and init the handler MOV DPTR,#0F060H ;Set our module ID to $F0, and the peer module ID to $60 MOV A,#0C1H ;discard all physical messages, as well as functional messages not from peer LCALL DLC_FILTER
Now that things are set up, we are ready to wait for a message. A message is displayed with the length byte first, then a dash, and then the message itself in hex digits.
MSG_LOOP: LCALL DLC_RX_READY ;check if new message is ready JNB ACC.0,MSG_LOOP ;wait if no message PUSH ACC ;save the result temporarily LCALL CRLF ;print a newline and scroll up previous messages MOV A,#buffer ;get buffer start adress MOV R0,A MOV A,@R0 ;get length byte from buffer MOV R7,A ;store length byte LCALL LCDHEX ;print out length in hex MOV A,#'-' LCALL CHROUT ;print separator character
Displaying the message contents is pretty straightforward and the code comments say it all...
MOV A,#buffer ;get buffer start MOV R0,A INC R0 ;skip length byte CJNE R7,#0,MSGOUT ;print a byte until end of message SJMP MSGEND ;goto end of message handling MSGOUT: MOV A,R0 PUSH ACC ;save pointer MOV A,@R0 ;get byte from buffer LCALL LCDHEX ;and print it in hex POP ACC MOV R0,A ;get pointer back INC R0 ;advance pointer DJNZ R7,MSGOUT ;continue for rest of message
Now that the bulk work is done, there are only a few details left to do:
MSGEND: POP ACC ;get back status of buffer JB ACC.1,MSG_OVF ;check if there was a buffer overflow MOV A,#'.' ;no, append a period to the message text SJMP NO_OVL MSG_OVF: MOV A,#'!' ;if overflow, append an exclamation mark NO_OVL: LCALL CHROUT LCALL DLC_UNLOAD_MSG ;remove message from buffer and prepare for next message LJMP MSG_LOOP
That's it! That wasn't so bad, was it? Now we can see all functional messages from module $60 (at least the first few bytes, depending on the LCD screen length). Since the length is evident and the source ID is not important, the next step could be not to print the length byte and source ID (because those are not important), but to instead print more of the message. This would be a nice exercise...
Here is the complete source file from this lesson (with the exception of all filtering being turned off), as well as the hex-file of this example.
Back to lesson 3 Click here to go to lesson 5
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