MSX System Variables

This is an overview of the system variables which you can use. They are official, unless mentioned otherwise.

VDP Registers: R#0-R#7, R#8-R#23, R#25-R#27, R#32-R#45 (not mirrored in system ram), S#0.

MSX System Variables located in Main ROM

Name	Address	Length	Description
CGTABL	#0004	2	Base address of the MSX character set in ROM
VDP.DR	#0006	1	Base port address for VDP data read
VDP.DW	#0007	1	Base port address for VDP data write
	#002B	1	Basic ROM version 7 6 5 4 3 2 1 0 │ │ │ │ └─┴─┴─┴── Character set │ │ │ │ 0 = Japanese, 1 = International, 2=Korean │ └─┴─┴────────── Date format │ 0 = Y-M-D, 1 = M-D-Y, 2 = D-M-Y └──────────────── Default interrupt frequency 0 = 60Hz, 1 = 50Hz
	#002C	1	Basic ROM version 7 6 5 4 3 2 1 0 │ │ │ │ └─┴─┴─┴── Keyboard type │ │ │ │ 0 = Japanese, 1 = International │ │ │ │ 2 = French (AZERTY), 3 = UK, 4 = German (DIN) └─┴─┴─┴────────── Basic version 0 = Japanese, 1 = International
	#002D	1	MSX version number 0 = MSX 1 1 = MSX 2 2 = MSX 2+ 3 = MSX turbo R
	#002E	1	Bit 0: if 1 then MSX-MIDI is present internally (MSX turbo R only)
	#002F	1	Reserved
CHAR_16	#0034	4	Default KANJI range. Copied to KANJTABLE by the DiskBIOS on boot.

MSX System Variables located in Sub ROM

Name	Address	Length	Description
	#0000	2	String "CD", identification of MSX Sub ROM
	#0002	2	Execution address for the startup screen on MSX 2, MSX 2+ or MSX turbo R. This is unofficial and undocumented.

MSX-DOS (DiskROM) System Variables located in RAM

These addresses are only initialized when a DiskROM is present (e.g. when the machine has a diskdrive or a harddisk interface connected).

Name	Address	Length	Description
KANJTABLE	#F30F	4	Two pairs of limits for the first bytes of Shift-JIS characters. See here and here for more information.
RAMAD0	#F341	1	Slot address of RAM in page 0 (DOS)
RAMAD1	#F342	1	Slot address of RAM in page 1 (DOS)
RAMAD2	#F343	1	Slot address of RAM in page 2 (DOS/BASIC)
RAMAD3	#F344	1	Slot address of RAM in page 3 (DOS/BASIC)
MASTER	#F348	1	Main DiskROM slot address

MSX System Variables located in RAM

This is the start of the MSX BIOS system area.

Name Address Length Description

RDPRIM #F380 5 Routine that reads from a primary slot

WRPRIM #F385 7 Routine that writes to a primary slot

CLPRIM #F38C 14 Routine that calls a routine in a primary slot

USRTAB #F39A 2 Address to call with Basic USR0

#F39C 2 Address to call with Basic USR1

#F39E 2 Address to call with Basic USR2

#F3A0 2 Address to call with Basic USR3

#F3A2 2 Address to call with Basic USR4

#F3A4 2 Address to call with Basic USR5

#F3A6 2 Address to call with Basic USR6

#F3A8 2 Address to call with Basic USR7

#F3AA 2 Address to call with Basic USR8

#F3AC 2 Address to call with Basic USR9

LINL40 #F3AE 1 Width for SCREEN 0 (default 37)

LINL32 #F3AF 1 Width for SCREEN 1 (default 29)

LINLEN #F3B0 1 Width for the current text mode

CRTCNT #F3B1 1 Number of lines on screen

CLMLST #F3B2 1 Column space. It’s uncertain what this address actually stores

TXTNAM #F3B3 2 BASE(0) - SCREEN 0 name table

TXTCOL #F3B5 2 BASE(1) - SCREEN 0 color table

TXTCGP #F3B7 2 BASE(2) - SCREEN 0 character pattern table

TXTATR #F3B9 2 BASE(3) - SCREEN 0 Sprite Attribute Table

TXTPAT #F3BB 2 BASE(4) - SCREEN 0 Sprite Pattern Table

T32NAM #F3BD 2 BASE(5) - SCREEN 1 name table

T32COL #F3BF 2 BASE(6) - SCREEN 1 color table

T32CGP #F3C1 2 BASE(7) - SCREEN 1 character pattern table

T32ATR #F3C3 2 BASE(8) - SCREEN 1 sprite attribute table

T32PAT #F3C5 2 BASE(9) - SCREEN 1 sprite pattern table

GRPNAM #F3C7 2 BASE(10) - SCREEN 2 name table

GRPCOL #F3C9 2 BASE(11) - SCREEN 2 color table

GRPCGP #F3CB 2 BASE(12) - SCREEN 2 character pattern table

GRPATR #F3CD 2 BASE(13) - SCREEN 2 sprite attribute table

GRPPAT #F3CF 2 BASE(14) - SCREEN 2 sprite pattern table

MLTNAM #F3D1 2 BASE(15) - SCREEN 3 name table

MLTCOL #F3D3 2 BASE(16) - SCREEN 3 color table

MLTCGP #F3D5 2 BASE(17) - SCREEN 3 character pattern table

MLTATR #F3D7 2 BASE(18) - SCREEN 3 sprite attribute table

MLTPAT #F3D9 2 BASE(19) - SCREEN 3 sprite pattern table

CLIKSW #F3DB 1 =0 when key press click disabled
=1 when key press click enabled
SCREEN ,,n will write to this address

CSRY #F3DC 1 Current row-position of the cursor

CSRX #F3DD 1 Current column-position of the cursor

CNSDFG #F3DE 1 =0 when function keys are not displayed
=1 when function keys are displayed

RG0SAV #F3DF 1 Mirror of VDP register 0 (Basic: VDP(0))

RG1SAV #F3E0 1 Mirror of VDP register 1 (Basic: VDP(1))

RG2SAV #F3E1 1 Mirror of VDP register 2 (Basic: VDP(2))

RG3SAV #F3E2 1 Mirror of VDP register 3 (Basic: VDP(3))

RG4SAV #F3E3 1 Mirror of VDP register 4 (Basic: VDP(4))

RG5SAV #F3E4 1 Mirror of VDP register 5 (Basic: VDP(5))

RG6SAV #F3E5 1 Mirror of VDP register 6 (Basic: VDP(6))

RG7SAV #F3E6 1 Mirror of VDP register 7 (Basic: VDP(7))

STATFL #F3E7 1 Mirror of VDP(8) status register (S#0)

TRGFLG

#F3E8

Information about trigger buttons and space bar state

7 6 5 4 3 2 1 0
│ │ │ │       └── Space bar, trig(0) (0 = pressed)
│ │ │ └────────── Stick 1, Trigger 1 (0 = pressed)
│ │ └──────────── Stick 1, Trigger 2 (0 = pressed)
│ └────────────── Stick 2, Trigger 1 (0 = pressed)
└──────────────── Stick 2, Trigger 2 (0 = pressed)

FORCLR #F3E9 1 Foreground color

BAKCLR #F3EA 1 Background color

BDRCLR #F3EB 1 Border color

MAXUPD #F3EC 3 Jump instruction used by Basic LINE command. The routines used are: RIGHTC, LEFTC, UPC and DOWNC

MINUPD #F3EF 3 Jump instruction used by Basic LINE command. The routines used are: RIGHTC, LEFTC, UPC and DOWNC

ATRBYT #F3F2 1 Attribute byte (for graphical routines it’s used to read the color)

QUEUES #F3F3 2 Queue table address, see QUETAB (initial value).

FRCNEW #F3F5 1 CLOAD flag
=0 when CLOAD
=255 when CLOAD?

SCNCNT #F3F6 1 Key scan timing
When it’s zero, the key scan routine will scan for pressed keys so characters can be written to the keyboard buffer

REPCNT #F3F7 1 This is the key repeat delay counter
When it reaches zero, the key will repeat

PUTPNT #F3F8 2 Address in the keyboard buffer where a character will be written

GETPNT #F3FA 2 Address in the keyboard buffer where the next character is read

CS120 #F3FC 5 Cassette I/O parameters to use for 1200 baud

CS240 #F401 5 Cassette I/O parameters to use for 2400 baud

LOW #F406 2 Signal delay when writing a 0 to tape

HIGH #F408 2 Signal delay when writing a 1 to tape

HEADER #F40A 1 Delay of tape header (sync.) block

ASPCT1 #F40B 2 Horizontal / Vertical aspect for CIRCLE command

ASPCT2 #F40D 2 Horizontal / Vertical aspect for CIRCLE command

ENDPRG #F40F 5 Pointer for the RESUME NEXT command

ERRFLG #F414 1 Basic Error code

LPTPOS #F415 1 Printer head position
Is read by Basic function LPOS and used by LPRINT Basic command

PRTFLG #F416 1 Printer output flag is read by OUTDO
=0 to print to screen
=1 to print to printer

NTMSXP #F417 1 Printer type is read by OUTDO. SCREEN ,,,n writes to this address
=0 for MSX printer
=1 for non-MSX printer

RAWPRT #F418 1 Raw printer output is read by OUTDO
=0 to convert tabs and unknown characters to spaces and remove graphical headers
=1 to send data just like it gets it

VLZADR #F419 2 Address of data that is temporarilly replaced by ‘O’ when Basic function VAL("") is running

VLZDAT #F41B 1 Original value that was in the address pointed to with VLZADR

CURLIN #F41C 2 Line number the Basic interpreter is working on, in direct mode it will be filled with #FFFF

QUETAB

#F959

Queue-table containing queue information. There are four queues in total, three PLAY queues and one RS232 queue, with 6-byte information blocks per queue:

0	Queue head offset (for writing).
1	Queue tail offset (for reading).
2	Flag indicating whether a byte has been returned.
3	Queue size.
4-5	Queue start address.

#F91F 1 Character set SlotID

#F920 2 Character set address

EXBRSA #FAF8 1 SUBROM slot address (EXtended Bios-Rom Slot Address)

XSAVE #FAFE 1 Light pen X coordinate read from the device (internal use only).

XOFFS

#FAFF

Light pen X calibration offset

Bit 0-6: X calibration offset
Bit 7: A light pen interrupt occurred. Used internally by the MSX-BIOS, user software mustn’t set it.

YSAVE #FB00 1 Light pen Y coordinate read from the device (internal use only).

YOFFS

#FB01

Light pen Y calibration offset

Bit 0-6: Y calibration offset
Bit 7: Reserved for future use. Mask from reads and do not set.

DRVINF #FB21 1 Nr. of drives connected to disk interface 1

#FB22 1 Slot address of disk interface 1

#FB23 1 Nr. of drives connected to disk interface 2

#FB24 1 Slot address of disk interface 2

#FB25 1 Nr. of drives connected to disk interface 3

#FB26 1 Slot address of disk interface 3

#FB27 1 Nr. of drives connected to disk interface 4

#FB28 1 Slot address of disk interface 4

EXPTBL #FCC1 1 Slot 0: #80 = expanded, 0 = not expanded. Also main BIOS-ROM slot address.

#FCC2 1 Slot 1: #80 = expanded, 0 = not expanded.

#FCC3 1 Slot 2: #80 = expanded, 0 = not expanded.

#FCC4 1 Slot 3: #80 = expanded, 0 = not expanded.

SLTTBL #FCC5 1 Mirror of slot 0 secondary slot selection register.

#FCC6 1 Mirror of slot 1 secondary slot selection register.

#FCC7 1 Mirror of slot 2 secondary slot selection register.

#FCC8 1 Mirror of slot 3 secondary slot selection register.

RG8SAV #FFE7 1 Mirror of VDP register 8 (Basic: VDP(9), note: +1)

RG9SAV #FFE8 1 Mirror of VDP register 9 (Basic: VDP(10), note: +1)

RG10SA #FFE9 1 Mirror of VDP register 10 (Basic: VDP(11), note: +1)

RG11SA #FFEA 1 Mirror of VDP register 11 (Basic: VDP(12), note: +1)

RG12SA #FFEB 1 Mirror of VDP register 12 (Basic: VDP(13), note: +1)

RG13SA #FFEC 1 Mirror of VDP register 13 (Basic: VDP(14), note: +1)

RG14SA #FFED 1 Mirror of VDP register 14 (Basic: VDP(15), note: +1)

RG15SA #FFEE 1 Mirror of VDP register 15 (Basic: VDP(16), note: +1)

RG16SA #FFEF 1 Mirror of VDP register 16 (Basic: VDP(17), note: +1)

RG17SA #FFF0 1 Mirror of VDP register 17 (Basic: VDP(18), note: +1)

RG18SA #FFF1 1 Mirror of VDP register 18 (Basic: VDP(19), note: +1)

RG19SA #FFF2 1 Mirror of VDP register 19 (Basic: VDP(20), note: +1)

RG20SA #FFF3 1 Mirror of VDP register 20 (Basic: VDP(21), note: +1)

RG21SA #FFF4 1 Mirror of VDP register 21 (Basic: VDP(22), note: +1)

RG22SA #FFF5 1 Mirror of VDP register 22 (Basic: VDP(23), note: +1)

RG23SA #FFF6 1 Mirror of VDP register 23 (Basic: VDP(24), note: +1)

ROMSLT #FFF7 1 Main BIOS slot ID. (MSX2 and up only)

RG25SA #FFFA 1 Mirror of VDP register 25 (Basic: VDP(26), note: +1)

RG26SA #FFFB 1 Mirror of VDP register 26 (Basic: VDP(27), note: +1)

RG27SA #FFFC 1 Mirror of VDP register 27 (Basic: VDP(28), note: +1)

#FFFD 2 Temporary stack pointer for CHGCPU.

#FFFF

Secondary slot select register, if the slot is expanded.

7 6 5 4 3 2 1 0
│ │ │ │ │ │ └─┴── Secondary slot for page 0 (#0000-#3FFF)
│ │ │ │ └─┴────── Secondary slot for page 1 (#4000-#7FFF)
│ │ └─┴────────── Secondary slot for page 2 (#8000-#BFFF)
└─┴────────────── Secondary slot for page 3 (#C000-#FFFF)

Reading returns the inverse of the current subslot selection. Values are mirrored in SLTTBL for convenience.

Note that each expanded primary slot has its own register. To access a specific primary slot’s register, you need to select it in page 3 before reading the value.

BiFi

MSX Assembly Page

MSX System Variables

MSX System Variables located in Main ROM

MSX System Variables located in Sub ROM

MSX-DOS (DiskROM) System Variables located in RAM

MSX System Variables located in RAM