Difference between revisions of "83Plus:Hooks:9B8C"

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'''Note:''' Do not take the information on this template page as actual documentation!
 
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The Hooks are named by their hook pointer block address (the four bytes consisting of page, address, and an extra byte), in hexadecimal. An example is [[83Plus:Hooks:9B84]].
 
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----
 
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== Synopsis ==
 
== Synopsis ==
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'''Name:''' ImAHook
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'''Name:''' Homescreen
  
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'''Hook Pointer Block Address:''' [[83Plus:RAM:8562|8562]]
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'''Hook Pointer Block Address:''' [[83Plus:RAM:9B8C|9B8C]]
  
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'''Hook Enable BCALL:''' [[83Plus:BCALLs:1234|1234]]
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'''Hook Enable BCALL:''' [[83Plus:BCALLs:4FAB|4FAB]]
  
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'''Hook Disable BCALL:''' [[83Plus:BCALLs:5678|5678]]
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'''Hook Disable BCALL:''' [[83Plus:BCALLs:4FAE|4FAE]]
  
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'''Hook Call BCALL:''' [[83Plus:BCALLs:9012|9012]]
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'''Hook Call BCALL:''' ''(none known)''
  
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'''Hook Active Flag:''' 6, (iy + 23h)
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'''Hook Active Flag:''' [[83Plus:Flags:34#Bit_4|4, (iy + 34h)]]
  
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This hook allows you to change the values that [[83Plus:BCALLs:4972|GetKey]] returns.
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This hook is called when various events occur on the homescreen.
  
 
== Using the Hook ==
 
== Using the Hook ==
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These different values, passed in a, determines what the hook should do.
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These different values, passed in A, determine what the hook should do.
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* 1: The calculator just turned on. There seem to be no other values passed to the hook.
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* 0: The calculator is displaying a result.
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* 2: The calculator is computing 1+1.
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** [[83Plus:RAM:8478|OP1]] = the value to display
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** b: 1
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** You can change the value in OP1 to display something different, which will not affect the value stored to Ans.
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** c: 1
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** If you want to display something wider than the screen, you must also write the formatted string to [[83Plus:RAM:97B1|fmtString]].
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** Change b and/or c to affect the output of the problem (which will still look like 1+1 to the user).
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** Return NZ and TIOS will not display anything.
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* 3: Preparing to turn off due to 2nd+OFF.
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* 1: A key was pressed at the homescreen.
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** Zero flag: Clear to abort the power off.
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** B = keycode
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** Change B to change the key that appears to be pressed.
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** Return NZ to ignore the keypress.
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* 2: An expression was entered to be evaluated.
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** OP1 contains the name of the entry, prgm#.
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** Return NZ to cancel running the program.
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* 3: Changing context to the homescreen.
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** B = previous context value
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** You should always return Z in this case.
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== Example ==
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The following code will display a random number as the result of any calculation.
  
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== Comments ==
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<nowiki>HomescreenHook:
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This hook doesn't exist. This is a demonstration only.
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        .db 83h            ; Required for all hooks
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        or a               ; are we in condition 0 (display value?)
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        jr nz,ReturnZ
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        B_CALL _Random      ; change our output value to a random #
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ReturnZ:
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        cp a                ; set zero condition
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        ret</nowiki>
  
 
== Credits and Contributions ==
 
== Credits and Contributions ==
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* '''/dev/hda1:''' My favorite hard drive partition.
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* '''Michael Vincent:''' Analysis and writing the most amazingly cool homescreen hacks I've seen yet.

Revision as of 23:14, 27 March 2005

Synopsis

Name: Homescreen

Hook Pointer Block Address: 9B8C

Hook Enable BCALL: 4FAB

Hook Disable BCALL: 4FAE

Hook Call BCALL: (none known)

Hook Active Flag: 4, (iy + 34h)

This hook is called when various events occur on the homescreen.

Using the Hook

These different values, passed in A, determine what the hook should do.

  • 0: The calculator is displaying a result.
    • OP1 = the value to display
    • You can change the value in OP1 to display something different, which will not affect the value stored to Ans.
    • If you want to display something wider than the screen, you must also write the formatted string to fmtString.
    • Return NZ and TIOS will not display anything.
  • 1: A key was pressed at the homescreen.
    • B = keycode
    • Change B to change the key that appears to be pressed.
    • Return NZ to ignore the keypress.
  • 2: An expression was entered to be evaluated.
    • OP1 contains the name of the entry, prgm#.
    • Return NZ to cancel running the program.
  • 3: Changing context to the homescreen.
    • B = previous context value
    • You should always return Z in this case.

Example

The following code will display a random number as the result of any calculation. 

HomescreenHook:
        .db 83h             ; Required for all hooks
        or a                ; are we in condition 0 (display value?)
        jr nz,ReturnZ
        B_CALL _Random      ; change our output value to a random #
ReturnZ:
        cp a                ; set zero condition
        ret

Credits and Contributions

  • Michael Vincent: Analysis and writing the most amazingly cool homescreen hacks I've seen yet.
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