Before we start you need some basic knowledge and tools I won't give you here. You need an 8032 assembler (there are many on the net), and you need to be able to program and erase a 27C256 EPROM. Of course you need to have some experience with the 8032/8052 series CPUs or at least some other assembly knowledge. If you have built your scantool board and see the "no application" message, you're ready to get started...
First you need to know how the ScanOS finds and starts an application program. ScanOS looks at the first 32 bytes of the external EPROM at address $8000. If the first two bytes contain values other than $A5, $02 the EPROM will not be recognized as a valid application program. The header contains your "reset vector" so to speak, everything has already been initialized, and you're ready to go, even the "screen" has been cleared. We will not worry about CRC calculation for now, so that has been disabled in this example.
Here's what a simple "Hello world" application would look like:
; ; simple "Hello World" program for ScanOS ; STROUT EQU 0106H ;vector of the string output routine ORG 08000H ;The external EPROM starts at address $8000 ;Application program header structure DB 0A5H ;"Magic" value, must be $A5 LJMP MAIN ;this is the starting address of your sample code DB 0,018H ;program length, only used for CRC calculation and loading DB 06EH,044H ;CRC, $6E44 DB 1 ;flag byte 1, set to 0 to disable CRC calculation DB 0 ;decompression mode: reserved DB 001H,05EH ;30-10-00 DB 0,0 ;no more files present DB 0,0 ;2 reserved bytes DB '1st program',0 ;up to 15 character program name plus nullbyte ORG 08020H MAIN: MOV DPTR,#STRING ;get the address of the string LCALL STROUT ;and print it out LOOP: SJMP LOOP ;wait here forever... STRING: DB 'Hello World!',13,10,0Click here to download the hex file for this example
Note: All future examples will no longer list the header structure, but instead will begin directly with the main entry point. Note that the sample code pieces presented on this and the following pages are only fragments and require the proper application program header and equates to run.
That wasn't so hard, was it? Now, let's get more serious and choose one of three different applications at startup. We'll present the user with a choice of three entries and branch to different areas of our ROM. For simplicity, I'll leave out the equates for the ScanOS function calls, they should be included in your source along with something similar to what you saw in the previous example. Let's just start at the "MAIN" label...
MAIN: MOV DPTR,#BOOT_SELECT ;pass the address of the menu structure LCALL SEL_MENU ;let the user make a choice CJNE A,#0FFH,VALID ;Did the user abort? SJMP MAIN ;yes: start over again! VALID: CJNE A,#0,SEL1 ;Did the user select entry #0 ? LJMP HELLO_WORLD ;Yes: branch to Hello World program SEL1: CJNE A,#1,SEL2 ;Or entry #1 ? LJMP PACMAN ;Yes: this is an exercise for the reader... SEL: LJMP SCANTOOL ;Well, nothing else left, let's do some scanning.. BOOT_SELECT: DB 3 ;Three entries total DB 0 ;Separator DB 'Hello World',0 ;Entry #0 DB 'PacMan',0 ;Entry #1 DB 'ScanTool',0 ;Entry #2
The last example for now is what we know from desktop computers as "Message boxes". This is a small message for the user that is usually just acknowledged or offers a simple selection between yes and no, or ok and cancel.
Prompting the user for such choices is really simple. The following code fragment displays a short message that the user can acknowledge or cancel. If the message does not fit the display, this function will try to format the message into multiple lines, and the user can scroll through the text before making a choice with the "*" (Cancel/No) or "#" (Ok/Yes/Enter) key.
ENTER EQU 13 LCDWIDTH EQU 16 MAIN: MOV DPTR,#MSG_TEXT ;This is a pointer to the message text MOV A,#LCDWIDTH ;This is the default length of the LCD display LCALL MESSAGE ;Display the message box and wait for user input. CJNE A,#13,GO_CANCEL ;Branch if the user did not answer "ok" ... MSG_TEXT: DB 'Do you wish to continue? | No=* Yes=#',0
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