Docs	Address	All machines	BBC Master 128
Page 00	0000	Current Language Zero Page	Master maps main ram even in shadow mode
0090	Operating System Zero Page
	0100	Processor Stack
Page 02	0200	Operating System Workspace
Page 03	0300
	0400	Current Language Workspace
0500
0600
0700
Page 08-0D	0800	Sound & Printer Buffer
0900	RS423, Speech & Tape output Buffer
0A00	RS423 & Tape input Buffer
0B00	Function Keys
0C00	User defined graphics
0D00	NMI routines (Disk/Econet)
0D9F	Expander vector set
0DF0	Paged ROM workspace storage locations
Page 0E-18	0E00	USER workspace	DFS workspace (not Master)
	1900
3000	Screen (Mode 0, 1, 2)	USER workspace with shadow Mode 128…134 Screen memory is in shadow ram at same addresses as on normal machines
4000	Screen (Mode 3)
5800	Screen (Mode 4, 5)
6000	Screen (Mode 6)
7B00	Screen (Mode 7)
Paged Rom	8000	Paged Roms	Private Ram
	C000	OS ROM	Paged rom workspace
DC00	MOS CLI Buffer
DD00	*MOVE workspace
DF00	MOS private workspace
E000	OS ROM
FC00	FRED 1MHz bus
FD00	JIM 1MHz bus
FE00	SHIELA I/O Memory
FF00	OS ROM Vectors

1 - Page 00

Address

Len

Description

0000

144

Allocated to current language

0070

32

Guaranteed unused with BASIC

0090

16

Econet workspace

00A0

8

Allocated to current NMI owner

00A8

8

OS command workspace

00B0

16

File system scratch space

00C0

16

File system private space

00D0

1

VDU status

Bit 0	VDU 2 enabled
Bit 1	Scroll disabled
Bit 2	Paged scroll selected
Bit 3	Soft scrolling
Bit 4	unused
Bit 5	VDU 5 enabled
Bit 6	Set when edit/text cursors are separated
Bit 7	Set if VDU driver disabled

00D1

1

Byte mask for current graphics point

00D2

2

Text colour to be ORed & EORed into memory respectively

00D4

2

Graphics colour to be ORed & EORed into memory respectively

00D6

2

Address of top line of current graphics character cell

00D8

1

Caps-lock/shift-lock

16	Shift lock
32	Caps lock
48	No locks

00DA

6

Temp workspace

00E0

2

Pointer to row multiplication table, high byte first

00E2

1

Cassette filing system status

Bit 0	Input file open
Bit 1	Output file open
Bit 2	Unused
Bit 3	Set if currently *CAT
Bit 4	Unused
Bit 5	Unused
Bit 6	Set if at end of file
Bit 7	Set if end of file warning issued

00E3

1

Cassette filing system options *OPT

00E4

3

General OS workspace

00E7

1

Auto repeat countdown timer

00E8

2

Pointer to input buffer used by OSWORD 0x01

00EA

1

RS423 timeout counter

<0	RS423 system holds 6850 but has not yet timed out
=0	RS423 system holds 6850 but has timed out
=1	Cassette filing system using 6850

00EB

1

Cassette critical flag

00EC

1

Internal key no of most recently pressed key

00ED

1

Internal key no of first key pressed of those still pressed

00EE

1

Internal key number of character to be ignored when scanning keyboard

Note	0xEE is also RAM copy of 1MHz bus register

00EF

1

Accumulator value for most recent OSBYTE/OSWORD

00F0

1

X register for most recent OSBYTE/OSWORD

00F1

1

Y register value for most recent OSBYTE/OSWORD

00F2

2

text pointer for processing OS commands/filenames

00F4

1

RAM copy of currently selected Paged ROM

00F5

1

Current logical speech PHROM or ROM filing system ROM number

00F6

2

Address pointer into paged ROM or speech PHROM

00F8

2

Unused

00FA

2

General OS workspace

00FC

1

Accumulator saved in IRQ routine

00FD

2

Pointer to error message

00FF

1

Escape status

Bit 7

set if ESCAPE pressed

On the BBC Micro addresses 0x0000…0x008F are reserved for the current language. The table above lists the known BASIC II memory map for those addresses.

BBC Basic reserves 0x0070…0x008F for user programs. User code should not use addresses outside that range unless they have replaced BASIC.

2 - Page 02

Address	Len	Name	Description
0200	2	USERV	User Vector
0202	2	BRKV	BRK Vector
0204	2	IRQ1V	Interrupt request Vector 1
0206	2	IRQ2V	Interrupt request Vector 2
0208	2	CLIV	OSCLI Vector
020A	2	BYTEV	OSBYTE Vector
020C	2	WORDV	OSWORD Vector
020E	2	WRCHV	OSWRCH Vector
0210	2	RDCHV	OSRDCH Vector
0212	2	FILEV	OSFILE Vector
0214	2	ARGSV	OSARGS Vector
0216	2	BGETV	OSBGET Vector
0218	2	BPUTV	OSBPUT Vector
021A	2	GBPBV	OSGBPB Vector
021C	2	FINDV	OSFIND Vector
021E	2	FSCV	File system control entry vector
0220	2	EVNTV	Event interrupt vector
0222	2	UPTV	User print routine vector
0224	2	NETV	Used by ECONET to take control of computer
0226	2	VDUV	Unrecognised VDU23 & PLOT commands
0228	2	KEYV	Full keyboard access
022A	2	INSV	Insert into buffer vector
022C	2	REMV	Remove from buffer vector
022E	2	CNPV	Count/purge buffer vector
0230	2	IND1V	Spare Vector
0232	2	IND2V	Spare Vector
0234	2	IND3V	Spare Vector
0236	2		Start address of OS variables
0238	2		Address of ROM pointer table
023A	2		Address of ROM information table
023C	2		Address of key translation table
023E	2		Start address of VDU variables
0240	1		CFS timeout counter
0241	1		Input source
0242	1		Keyboard semaphore
0243	1		Primary OSHWM
0244	1		Current OSHWM
0245	1		RS423 mode
0246	1		Character definition explosion state
0247	1		Cassette/ROM filing system switch
0248	1		RAM copy of ULA control reg
0249	1		RAM copy of ULA palette reg
024A	1		ROM number active at last BRK
024B	1		ROM number containing BASIC
024C	1		Current ADC channel
024D	1		Max ADC channel
024E	1		ADC conversion type
024F	1		RS423 user flag
0250	1		RS423 control flag
0251	1		Flashing colours counter
0252	1		Mark period counter
0253	1		Space period counter
0254	1		Keyboard auto-repeat delay
0255	1		Keyboard auto-repeat period
0256	1		*EXEC file handle
0257	1		*SPOOL file handle
0258	1		ESCAPE/BREAK effect
0259	1		ECONET keyboard disable
025A	1		Keyboard status
025B	1		RS423 handshake extent
025C	1		RS423 input supression flag
025D	1		RS423/cassette selection flag
025E	1		Econet OS call interception status
025F	1		Econet OSRDCH interception status
0260	1		Econet OSWRCH interception status
0261	1		Speech suppression status
0262	1		Sount suppression status
0263	1		BELL channel
0264	1		BELL envelope number/volume
0265	1		BELL frequency
0266	1		BELL duration
0267	1		Startup message & !BOOT options
0268	1		Length of soft key string
0269	1		No of lines printed since last page
026A	1		No of items in VDU queue
026B	1		TAB character value
026C	1		ESCAPE character value
026D	1		Character 0xC0 to 0xCF status
026E	1		Character 0xD0 to 0xDF status
026F	1		Character 0xE0 to 0xEF status
0270	1		Character 0xF0 to 0xFF status
0271	1		Function key status
0272	1		SHIFT+Function key status
0273	1		CTRL+Function key status
0274	1		CTRL+SHIFT+Function key status
0275	1		ESCAPE key status
0276	1		ESCAPE key effect
0277	1		IRQ bit mask for user 6522
0278	1		IRQ bit mask for 6850
0279	1		IRQ bit mask for system 6522
027A	1		Tube presence flag
027B	1		Speech processor presence flag
027C	1		Write character destination status
027D	1		Cursor editing status
027E	3		Unused
0281	1		Used by *FX1
0282	1		RAM copy of serial processor ULA
0283	1		Timer switch state
0284	1		Soft key consistancy flag
0285	1		Printer destination flag
0286	1		Character ignored by printer
0287	3		BREAK intercept code
028A	2		Unused
028C	1		Current language ROM number
028D	1		Last BREAK type
028E	1		Available RAM
028F	1		Start up option flag
0290	1		VDU vertical adjust, set by *TV
0291	1		Interlace toggle flag, set by *TV
0292	5		First copy of system clock values
0297	5		Second copy of system clock values
029C	5		Countdown interval timer value
02A1	16		Paged ROM type table
02B1	2		INKEY countdown timer
02B3	3		OSWORD 0x01 workspace
02B6	4		Low bytes of most recent analogue converter values
02BA	4		High bytes of most recent analogue converter values
02BE	1		Analogue system flag
02BF	10		Event enable flags
02C9	1		Soft key expansion pointer
02CA	1		First auto repeat count
02CB	3		Two key rollover processing workspace
02CE	1		Sound semaphore
02CF	9		Buffer busy flags
02D8	9		Buffer start indices
02E1	9		Buffer end indices
02EA	2		Block size of current resident block of open cassette input file
02EC	1		Block flag of current resident block of open cassette input file
02ED	1		Last character in currently resident block of open cassette input file
02EE	18		Used as area to build OSFILE control blocks for LOAD & SAVE

3 - Page 03

Address

Len

Description

0300

2

X/Right coordinate of graphics window

0302

2

Y/Bottom coordinate of graphics window

0304

2

X/left coordinate of graphics window

0306

2

Y/Top coordinate of graphics window

0308

1

X/left of text window

0309

1

Y/bottom of text window

030A

1

X/right of text window

030B

1

Y/top of text window

030C

2

X coordinate of graphics origin

030E

2

Y coordinate of graphics origin

0310

4

Current graphics origin in external coordinates

0314

4

Current graphics cursor in external coordinates

0318

1

Text cursor X coordinate

0319

1

Text cursor Y coordinate

031A

1

Line within current graphics char of graphics point

031B

4

Graphic workspace or start of VDU queue

031F

5

VDU queue

0324

4

Current graphics cursor in internal coordinates

033C

2

Graphics cursor Y coordinate

033E

2

Graphics cursor X coordinate

034A

2

Text cursor address

034C

2

Text window width in bytes

034E

1

High byte of screen memory start address, Low is 0x00

034F

1

Bytes per character

0350

2

Address of top-left of screen

0352

2

No bytes per line

0354

1

Screen memory length

0355

1

Mode

0356

1

Screen memory map type

0357

1

Foreground text colour

0358

1

Background text colour

0359

1

Graphics foreground mask

035A

1

Graphics background mask

035B

1

Graphics foreground modifier

035C

1

Graphics background modifier

035D

2

General VDU jump vector

035F

1

Record of last setting of 6845 cursor start reg

0360

1

No colours available

0361

1

No of pixels per byte

0362

2

left/right colour masks

0364

2

Text input cursor coordinates

0366

1

Teletext output cursor character

0367

1

Font flag (RAM or ROM)

Bit 1	Characters 224-255
Bit 2	Characters 192-223
Bit 3	Characters 160-191
Bit 4	Characters 128-159
Bit 5	Characters 96-127
Bit 6	Characters 64-95
Bit 7	Characters 32-63

0368

7

Font location bytes

036F

16

Palette mapping actual colour for each logical colour

0380

29

Header block for BPUT file store

039D

1

Offset of next byte to be output into BPUT buffer

039E

1

Offset of next byte to be read from BGET buffer

039F

8

Unused

03A7

11

Filename of file being BGETed

03B2

31

Block header of most recent block read

03B2

12

Filename terminated by zero

03BE

4

Load address

03C2

4

Exec address

03C6

2

Block number address

03C8

2

Block length

03CA

1

Block flag byte

03CB

4

4 spare bytes

03CF

2

Checksum

03D1

1

Sequential block gap, *OPT3

03D2

11

Filename of file being searched for

03DD

2

Number of next block expected for BGET

03DF

1

Copy of block flag of last block read

03E0

32

Runtime keyboard buffer

4 - Page 08-0D

Address	Len	Description
0800	64	Sound workspace
0840	16	Sound channel 0 buffer
0850	16	Sound channel 1 buffer
0860	16	Sound channel 2 buffer
0870	16	Sound channel 3 buffer
0880	64	Printer buffer
08C0	64	Envelope storage area, envelopes 1-4
0900	192	RS423 output buffer or Envelope storage area, envelopes 5-16
09C0	64	Speech buffer
0900	256	Cassette output buffer (takes entire page if used)
0A00	256	RS423 or Cassette input buffer
0B00	16	1 byte pointer to *KEY text for soft keys 0-15
0B10	240	Function key text
0C00	256	Character 224-255 definitions
0D00	159	NMI routines (disk & econet)
0D9F	121	Expander vector set
0DF0	16	Paged ROM workspace storage locations

5 - Page 0E-18 DFS

Address	Len	Description
0E00	256	Copy of track 0 sector 0 catalogue data
0F00	256	Copy of track 0 sector 1 catalogue data
1000	256	Workspace
1100	256	Parameter blocks for files/SPOOL/EXEC
1200	256	First file/SPOOL/EXEC buffer
1300	256	Second file buffer
1400	256	Third file buffer
1500	256	Fourth file buffer
1600	256	Fifth file buffer
1700	256	Workspace
1800	256	Workspace

This table relates to a BBC Model B with Acorn DFS active. This will use pages 0x0E to 0x18 with the USER workspace starting at page 0x19.

This does NOT apply when either the Cassette or ROM filesystem is active, or on a BBC Master 128. In those cases USER workspace starts at page 0x0E.

6 - Paged Roms

Paged roms exist within the 16K address block 0x8000…0xBFFF.

The following table shows the layout of the Paged Roms on a Standard Machines

Rom #		BBC A & B	BBC B+	Master 128	Master Compact	Acorn Electron
15	F	IC101 AUX ROM, usually Basic or Basic II	IC71 BASIC II or Sideways RAM (B+ 128K only)	Terminal	Utilities	External ROM +1, Slogger etc
14	E	IC100 AUX ROM usually empty	IC71 BASIC II or Sideways RAM (B+ 128K only)	View	BASIC IV
13	D	IC88 "Disk & Net ROM" typically empty	Sideways RAM (B+ 128K only)	ADFS	ADFS 2.10
12	C	IC52 BASIC ROM typically containing DFS	Sideways RAM (B+ 128K only)	Basic	System top 16k
11	B	Mapped to slot 0xF	IC68 DFS 2.26 + SRAM 1.05	Edit	System 2nd 16k	IC 2 BASIC II
10	A	Mapped to slot 0xE	IC68 DFS 2.26 + SRAM 1.05	Viewsheet	System 3rd 16k	IC 2 BASIC II
9	9	Mapped to slot 0xD	IC62 RAM	DFS	System 4th 16k	Keyboard is mapped here
8	8	Mapped to slot 0xC	IC62 RAM	IC27 Internal Socket	IC29	Keyboard is mapped here
7	7	Mapped to slot 0xF	IC57 RAM	RAM or IC37	RAM	External ROM Internal rom must be disabled use *FX142,n to select
6	6	Mapped to slot 0xE	IC57 RAM	RAM or IC37	RAM
5	5	Mapped to slot 0xD	IC44 RAM	RAM or IC41	RAM
4	4	Mapped to slot 0xC	IC44 RAM	RAM or IC41	RAM
3	3	Mapped to slot 0xF	IC35 RAM	SK4 Front Cartridge slot	IC17
2	2	Mapped to slot 0xE	IC35 RAM	SK4 Front Cartridge slot	IC23
1	1	Mapped to slot 0xD	Sideways RAM (B+128K only) or BASIC II (alternate location)	SK3 Rear Cartridge slot	IC38 or expansion port
0	0	Mapped to slot 0xC	Sideways RAM (B+128K only) or BASIC II (alternate location)	SK3 Rear Cartridge slot	IC38 or expansion port