Finally, you've made it. Now we will examine a sample program that displays a data stream from a mid-eighties C3 ECM.
First, we need to reserve some space for a receive buffer, and initialize ScanOS to look for a C3 data stream. The stream we're looking at will contain 25 bytes per frame, so that's the buffer size we'll reserve.
ORG 048H buffer: DS 25 ; MAIN: LCALL MODE_10K ;switch ECM into 10K mode to initiate diagnostic data stream. ; MOV DPTR,#buffer ;pass buffer address MOV A,#25 ;and frame/buffer size LCALL INIT_C3 ;to ScanOS and initialize the receive handler ; LOOP: LCALL C3_TESTLOCK ;check if ScanOS has locked on to the data stream CJNE A,#0,START SJMP LOOP ;wait until communication has been established
That's all there is to it! Now ScanOS will constantly read the frames it receives into the provided buffer.
Now we want to display and update the battery voltage from the data stream. We will use the function Slot_DispItem to display the data "item" from the stream. This function monitors the buffer for a new frame, and if a new frame has been received, it clears the screen and outputs the new value. In this data stream, the battery voltage is in byte 17 of the buffer (counting from zero) and ranges from 0 to 25.5 volts.
The "item" description is passed via a pointer that refers to a structure describing how the display should be formatted. It sounds difficult, but it's not. All you need to define are which byte in RAM contains what you want to output, how to interpret the data and two strings; one to be printed before the item, and one after it. The strings may also contain CR and LF characters, so you can use the full 2x16 LCD screen to display your data in a meaningful way.
Slot_DispItem will return when the user presses a key.
START: MOV DPTR,#S_BAT ;Point to a structure describing the battery "item" LCALL SLOT_DISPITEM ;display "item" on LCD until user presses a key ; LCALL EXIT_C3 ;we're done, clean up S: SJMP S ;wait here forever ; S_BAT: DB buffer+17 ;memory location containing "item", in this case battery voltage DB 3 ;display routine to use: 3 = byte * 0.1 DB 'Battery: ',0 ;string to display before data value DB ' V',0 ;string to display after data value
You see, it can't be much simpler. Of course, this is a pretty "dumb" scantool application. It only watches one byte in the data stream. But with the Sel_Menu function you can easily have the user select one of several choices, and use the result to load one of several description pointers into Slot_Dispitem. And after the user presses a key, it's not very smart to "hang", but, again, this is just a demo code snippet. Use your imagination. Or take a look at the application program in the next and final lesson, and take it from there.
If you don't like Slot_Dispitem and want to display more than one value at the same time, you can still use Slot_Output to display just one byte from the buffer and have it formatted, but then you'll have to take care of when to refresh, waiting for the next frame, etc.
Well, I'm glad you asked. As far as ScanOS is concerned, you just use a different init function, and you also need to pass the module ID of the module you're interested in:
MOV DPTR,#buffer MOV A,#67 ;The buffer needs to be bigger for the P4 MOV R0,#0F0H ;This is the module ID we're expecting (usually F0 or F4) LCALL UART_INIT ;Initialize the UART handler ; ;... display the contents of the buffer here as above ; LCALL UART_EXIT ;Clean up S: SJMP S ;"hang"
So you see, it's not much different. One noteworthy thing though: some ECMs don't spill out their guts if you just switch to 10K mode, instead they must be sent a command frame to initiate data transmission. ScanOS has the function UART_Tx_Msg to do just that, but I could not test that function since I don't have access to an ECM with that feature. This is something left for your experiments...
Back to lesson 4 Click here to go to lesson 6
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