z80:System Flags

The system flags are a special place in memory pointed to by the IY index register, which points to flags. They contain vital information that can be stored in 1 bit, so they have been compressed into 1 bit to save space. If you ever need to restore the IY register back before quiting, do this:

   ld IY,flags

To do something to the flags (set, reset, or bit), do this:

   set trigDeg,(IY+trigFlags)                  ;trigDeg is now 1
   res trigDeg,(IY+trigFlags)                  ;trigDeg is now 0
   bit trigDeg,(IY+trigFlags)                  ;Tests trigDeg

Assembly Flags

If you look at the bottom of the flags table, you'll notice that there are 3 bytes for assembly flags. These are flags that are not used by the OS, and can be used by assembly programmers for their own purposes.

   #define shoot asm_Flag1_0
   # define weaponFlags asm_Flag1

System Flags Breakdown

Here's a breakdown of the system flags:

Flag Name	IY Offset	Equate Description	Comments
trigDeg	trigFlags	0 = radian angle mode
		1 = degree angle mode
plotLoc	plotFlags	0 = write to display and buffer
		1 = write to display only
plotDisp	plotFlags	0 = graph screen not in display
		1 = graph in display
grfFuncM	grfModeFlags	0 = not function graph mode	Please note that the grfMode functions must have only 1 set and the rest reset; otherwise, the calculator will crash.
		1 = function graph mode
grfPolarM	grfModeFlags	0 = not polar graph mode	Please note that the grfMode functions must have only 1 set and the rest reset.
		1 = polar graph mode
grfParamM	grfModeFlags	0 = not parametric graph mode	Please note that the grfMode functions must have only 1 set and the rest reset.
		1 = parametric graph mode
grfRecurM	graphFlags	0 = not sequence graph mode	Please note that the grfMode functions must have only 1 set and the rest reset.
		1 = sequence graph mode
graphDraw	grfDBFlags	0 = graph is up to date
		1 = graph needs to be updated
grfDot	grfDBFlags	0 = graph connected draw mode
		1 = graph dot draw mode
grfSimul	grfDBFlags	0 = Draw functions one at a time
		1 = Draw all functions simultaneously
grfGrid	grfDBFlags	0 = graph mode grid off
		1 = graph mode grid on
grfPolar	grfDBFlags	0 = Rectangular coordinates
		1 = Polar coordinates
grfNoCoord	grfDBFlags	0 = graph coordinates off
		1 = graph coordinates on
grfNoAxis	grfDBFlags	0 = graph draw axis
		1 = graph no axis
grfLabel	grfDBFlags	0 = graph labels off
		1 = graph labels on
textEraseBelow	textFlags	0 = Don't erase line below	Only on small text
		1 = erase line below
textInverse	textFlags	0 = Regular text	Affects both small and large text
		1 = write in reverse video
onInterrupt	onFlags	0 = No on-key interrupt	The on-key is interrupt driven but doesn't stop execution. Flag is set by the interrupt handler when the on-key is pressed.
		1 = On-key interrupt encountered
statsValid	statFlags	0 = Stat results invalid
		1 = Stat results valid
fmtExponent	cell-content	0 = Normal Mode	Either fmtExponent, fmtEng, or neither is set.
		1 = scientific display mode
fmtEng	fmtFlags	0 = Normal Mode	Either fmtExponent, fmtEng, or neither is set.
		1 = engineering display mode
fmtReal	fmtFlags	0 = Not real math mode	Either fmtReal, fmtRect,or fmtPolar must be set
		1 = real math mode
fmtRect	fmtFlags	0 = Not rect complex math mode	Either fmtReal, fmtRect,or fmtPolar must be set
		1 = rect complex math mode
fmtPolar	fmtFlags	0 = not polar complex math mode	Either fmtReal, fmtRect,or fmtPolar must be set
		1 = polar complex math mode
curAble	curFlags	0 = Cursor flash disabled
		1 = Cursor flash enabled
curOn	curFlags	0 = Invisible cursor
		1 = cursor is showing
curLock	curFlags	0 = Cursor not locked
		1 = Cursor is locked off
appTextSave	appFlags	0 = Don't write to textShadow	Places a copy of the character written to the display into the textShadow buffer.
		1 = Save characters written in textShadow
appAutoScroll	appFlags	0 = Don't auto scroll	Scrolls text if on last line of large text
		1 = auto-scroll text on last line
indicRun	indicFlags	0 = run indicator off
		1 = run indicator on
comFailed	getSendFlg	0 = com did not fail
		1 = com failed
apdRunning	apdFlags	0 = APD off
		1 = APD on
indicOnly	indicFlags	0 = Run indicator not only priority	Sets the interrupt handler to update the run indicator, but not to process APD, blink the cursor, or scan for keys. It is useful when executing I/O link port operations for speed.
		1 = only update run indicator
shift2nd	shiftFlags	0 = second key not pressed
		1 = second key pressed
shiftAlpha	shiftFlags	0 = Normal mode
		1 = Alpha mode
shifLwrAlpha	shiftFlags	0 = not lowercase mode	Alpha mode also active if set
		1 = lower case mode
shiftALock	shiftFlags	0 = Not Alpha lock	Alpha mode also set
		1 = Alpha lock
grfSplit	sGrFlags	0 = Normal graph mode	Either grfSplit, vertSplit, or neither must be set
		1 = horizontal graph split mode
vertSplit	sGrFlags	0 = Normal graph mode	Either grfSplit, vertSplit, or neither must be set
		1 = vertical graph split mode
textWrite	sGrFlags	0 = small font writes to display
		1 = small font writes to buffer
fullScrnDraw	apiFlag4	0 = Can't use column 95 or row 0
		1 = allows draws to use column 95 and row 0
bufferOnly	plotFlag3	0 = Draw to display and buffer
		1 = draw to graph buffer only
fracDrawLFont	fontFlags	0 = small font with UserPutMap	Affects small text routines
		1 = draw large font in UserPutMap
customFont	fontFlags	0 = Standard OS fonts
		1 = draw custom characters
lwrCaseActive	appLwrCaseFlag	0 = Lowercase disabled for GetKey
		1 = enable lower case in GetKey loop
asm_Flag1_0	asm_Flag1	Your choice	Not used by the OS.
asm_Flag1_1	asm_Flag1	Your choice	Not used by the OS.
asm_Flag1_2	asm_Flag1	Your choice	Not used by the OS.
asm_Flag1_3	asm_Flag1	Your choice	Not used by the OS.
asm_Flag1_4	asm_Flag1	Your choice	Not used by the OS.
asm_Flag1_5	asm_Flag1	Your choice	Not used by the OS.
asm_Flag1_6	asm_Flag1	Your choice	Not used by the OS.
asm_Flag1_7	asm_Flag1	Your choice	Not used by the OS.
asm_Flag2_0	asm_Flag2	Your choice	Not used by the OS.
asm_Flag2_1	asm_Flag2	Your choice	Not used by the OS.
asm_Flag2_2	asm_Flag2	Your choice	Not used by the OS.
asm_Flag2_3	asm_Flag2	Your choice	Not used by the OS.
asm_Flag2_4	asm_Flag2	Your choice	Not used by the OS.
asm_Flag2_5	asm_Flag2	Your choice	Not used by the OS.
asm_Flag2_6	asm_Flag2	Your choice	Not used by the OS.
asm_Flag2_7	asm_Flag2	Your choice	Not used by the OS.
asm_Flag3_0	asm_Flag3	Your choice	Not used by the OS.
asm_Flag3_1	asm_Flag3	Your choice	Not used by the OS.
asm_Flag3_2	asm_Flag3	Your choice	Not used by the OS.
asm_Flag3_3	asm_Flag3	Your choice	Not used by the OS.
asm_Flag3_4	asm_Flag3	Your choice	Not used by the OS.
asm_Flag3_5	asm_Flag3	Your choice	Not used by the OS.
asm_Flag3_6	asm_Flag3	Your choice	Not used by the OS.

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