Kernal Jump Table

A.C. Wright 6502 BIOS
Kernal · BIOS v1.5

The contract

Call the slot, never the implementation. 53 entry points, three bytes each, starting at $A000 and in an order that does not change. jsr $A000 prints a character on this ROM and on the next one. 6502.inc gives every slot its name, so you will write jsr Chrout.

Arguments go in registers. A, X and Y in, A, X, Y or the carry flag out. Nothing is passed on the stack.

The tail of the table. 32 slots from $A09F to $A0FE are reserved. Each is a real jump to a bare RTS, so calling one is harmless now and may do something later. Do not put your own code there.

Console

Addr	Name	In / out
$A000	Chrout	Output char (dispatched by IO_MODE) in A = character to output
$A003	Chrin	Input char from buffer
$A090	PrintStr	Print NUL-terminated string (A=lo, Y=hi); clobbers A,Y,STR_PTR in A = string address low, Y = string address high · out A, Y clobbered; X preserved; clobbers STR_PTR (Chrout preserves it)
$A093	PrintCRLF	Print CR+LF
$A096	PrintDecU16	Print unsigned 16-bit decimal (A=lo, X=hi), no leading zeros in A = value low, X = value high
$A006	WriteBuffer	Write byte to input buffer
$A009	ReadBuffer	Read byte from input buffer
$A00C	BufferSize	Get buffer count
$A00F	SetIOMode	Set IO_MODE in A = mode (bit 0: 0=video, 1=serial)
$A012	GetIOMode	Get IO_MODE out A = current IO_MODE

The screen

Addr	Name	In / out
$A015	InitVideo	Initialize TMS9918 (mode registers + character set)
$A018	VideoClear	Clear video screen
$A01B	VideoPutChar	Write char at cursor in A = character to write
$A02A	VideoChroutRaw	Output char to video (raw, no control-code handling) in A = character code (0-255)
$A01E	VideoSetCursor	Set cursor (X=col, Y=row) in X = column (0-39), Y = row (0-23)
$A021	VideoGetCursor	Get cursor position out X = column (0-39), Y = row (0-23)
$A024	VideoScroll	Scroll screen up one line
$A027	VideoSetColor	Set TMS9918 text color (A=reg7 byte: hi=fg, lo=bg) in A = color byte (high nibble = fg color, low nibble = bg color)

Sound

Addr	Name	In / out
$A02D	InitSID	Initialize SID
$A030	Beep	Play beep tone
$A033	SidPlayNote	Play note (A=voice, X=freqLo, Y=freqHi) in A = voice (0-2), X = frequency low byte, Y = frequency high byte
$A036	SidSilence	Silence all voices
$A039	SidSetVolume	Set SID master volume (A=0-15) in A = volume (0-15); upper nibble of SID_MODE_VOL is cleared (no filter)

Keyboard and sticks

Addr	Name	In / out
$A045	InitKB	Initialize GPIO/VIA keyboard
$A048	ReadJoystick1	Read joystick 1 out A = joystick bitmask (active-low bits: R-L-D-U-Y-X-B-A)
$A04B	ReadJoystick2	Read joystick 2 out A = joystick bitmask (active-low bits: R-L-D-U-Y-X-B-A)
$A099	KBDisable	Release both encoders and settle; ports free for raw read
$A09C	KBEnable	Re-enable both encoders

Kernal Jump Table

A.C. Wright 6502 BIOS
Kernal · BIOS v1.5

Files

Addr	Name	In / out
$A07E	FsLoadFileAddr	Load named file to FS_IO_ADDR in STR_PTR = filename, FS_IO_ADDR = destination address
$A081	FsSaveFileAddr	Save FS_FILE_SIZE bytes from FS_IO_ADDR to named file in STR_PTR = filename, FS_IO_ADDR = source address, FS_FILE_SIZE = byte count
$A03C	FsLoadFile	Load file from CF in STR_PTR ($02-$03) points to null-terminated filename · out Carry clear = success, FS_FILE_SIZE = bytes loaded; Carry set = file not found or read error
$A03F	FsSaveFile	Save file to CF in STR_PTR ($02-$03) points to null-terminated filename; FS_FILE_SIZE ($034A-$034B) = number of bytes to save · out Carry clear = success, Carry set = error (directory full or write error)
$A042	FsDeleteFile	Delete file from CF in STR_PTR ($02-$03) points to null-terminated filename · out Carry clear = success, Carry set = file not found or error
$A084	FsFormatDisk	Zero the current disk's directory sector out Carry clear = success, Carry set = write error
$A087	FsSetDisk	Select current CF disk (A=0-255) in A = disk number (0-255)
$A08A	FsGetDisk	Get current CF disk (A=disk) out A = current disk number
$A08D	FsPrintDisk	Print "DISK n" + CRLF via Chrout

The card itself

Addr	Name	In / out
$A06C	StReadSector	Read CF sector in CF_LBA ($26-$29) = LBA address, CF_BUF_PTR ($24-$25) = destination pointer · out Carry clear = success, Carry set = error; CF_BUF_PTR advanced by 512 bytes on success
$A06F	StWriteSector	Write CF sector in CF_LBA ($26-$29) = LBA address, CF_BUF_PTR ($24-$25) = source pointer · out Carry clear = success, Carry set = error; CF_BUF_PTR advanced by 512 bytes on success
$A072	StWaitReady	Wait CF ready out Carry clear = ready, Carry set = error or timeout

Serial

Addr	Name	In / out
$A04E	InitSC	Initialize serial 6551
$A051	SerialChrout	Direct serial output (bypass IO_MODE)
$A054	XModemLoad	Receive binary via XModem in XFER_PTR = destination address (set by caller) · out Carry clear = success, XFER_PTR past last byte written; XFER_REMAIN = total bytes received; Carry set = transfer failed
$A057	XModemSave	Send binary via XModem in XFER_PTR = source address, XFER_REMAIN = byte count (set by caller) · out Carry clear = success, Carry set = transfer failed

Clock and lasting memory

Addr	Name	In / out
$A05A	RtcReadTime	Read RTC time out A = hours (binary), X = minutes (binary), Y = seconds (binary)
$A05D	RtcReadDate	Read RTC date out A = day of month (binary), X = month (binary), Y = year (binary); RTC_BUF_CENT = century (binary)
$A060	RtcWriteTime	Set RTC time in A = hours (binary), X = minutes (binary), Y = seconds (binary)
$A063	RtcWriteDate	Set RTC date in A = day of month (binary), X = month (binary), Y = year (binary); RTC_BUF_CENT = century (binary)
$A066	RtcReadNVRAM	Read NVRAM byte in X = NVRAM address ($00-$FF) · out A = data byte
$A069	RtcWriteNVRAM	Write NVRAM byte in X = NVRAM address ($00-$FF), A = data byte

The machine

Addr	Name	In / out
$A075	SysDelay	Delay A=cnt_lo, X=cnt_hi centiseconds in A = count low byte, X = count high byte
$A078	KernalInit	Initialize all hardware (caller must reset SP; no cli, no splash); rts when done
$A07B	KernalVersion	Get BIOS version (A=major, X=minor) out A = major version, X = minor version