OsByte Calls
			    ============

A=&00 (0)	Return Operating System Number
On entry:
	X=0	Execute error giving OS version message, error number 247
	X<>0	Returns OS number in X
On exit:		
	If X<>&80 on entry:
	X=0	OS 1.00 - Early BBC, Electon OS 1.00
	X=1	OS 1.20 - BBC B or American MOS
	X=2	OS 2.00 - BBC B+
	X=3	OS 3.2x - Master 128
	X=4	OS 4.00 - Master ET
	X=5	OS 5.00 - Master Compact
	X=6	OS 6.00 - Archimedes
	X=7		  Springboard
	X=8		  UNIX
	X=32		  BBCBASIC(86) running on an IBM PC
BBCBASIC(86) implements all OsByte calls as OsByte 135/&87, Read character
at text position.  This usually returns 32 (space).
	If X=&80 on entry:
	X<&40	No response to call, OS version same as above
	X>&3F	OS version sub-number plus &40	


A=&01 (1)	User OsByte Call/Program Return Value
On entry:
	X=value to set user variable to
On exit:
	X=old value


A=&02 (2)	Select input stream
On entry:
	X=0	Keyboard selected, RS232 disabled
	X=1	RS232 selected and enabled
	X=2	Keyboard selected, RS232 enabled
On exit:
	X=corrupted


A=&03 (3)	Select output stream
On entry:
	X determines the output stream as follows:
	bit 0	Enables RS232 driver
	bit 1	Disables VDU driver
	bit 2	Disables printer driver
	bit 3	Enables printer, independant of VDU 2 or 3
	bit 4	Disables spooled output
	bit 5	not used
	bit 6	Disables printer driver unless preceded by VDU 1
	bit 7	not used
On exit:
	X=old value


A=&04 (4)	Set cursor editing state
On entry:
	X=0	Enable cursor editing (default)
	X=1	Editing keys give ASCII codes &87 to &8B
	X=2	Editing keys are soft keys 11 to 15
	X=3	Cursor keys have joystick effect, COPY is fire (Compact)
On exit:
	X=previous state

A=&05 (5)	Select printer destination

This call flushes the printer buffer and selects a new printer.  The
destination is not reset on a soft Break.
On entry:
	X=0	printer sink
	X=1	Parallel printer, Centronics port
	X=2	Serial printer, RS232 port
	X=3	User printer
	X=4	Network printer
	X>4	User printer
On exit:
	X=previous printer destination


A=&06 (6)	Select printer ignore character
On entry:
	X=character to be ignored
On exit:
	X=previous setting


A=&07 (7)	Set RS232 receive rate
A=&08 (8)	Set RS232 transmit rate
On entry:
	X=0
	X=1	75 baud
	X=2	150 baud
	X=3	300 baud
	X=4	1200 baud
	X=5	2400 baud
	X=6	4800 baud
	X=7	9600 baud
	X=8	19200 baud
On exit:
	YX contain old serial ULA contents


A=&09 (9)	Set mark duration of flashing colours

This call sets the duration of the mark state of flashing colours, ie the
duration of the first named colour.

On entry:
	X=0	Sets to infinity.  Forces mark state if space set to zero.
	X<>0	Sets mark duration in centiseconds (default 25)
On exit:
	X=old mark duration


A=&0A (10)	Set space duration of flashing colours

This call sets the duratin of the space state of flashing colours, ie the
duration of the second named colour.

On entry:
	X=0	Sets to infinity.  Forces space state if mark set to zero.
	X<>0	Sets space duration in centiseconds (default 25)








A=&7E (126)	Acknowledge ESCAPE with effects

This call attempts to clear the Escape condition.  All active buffers will
be flushed, any open EXEC file will be closed and the VDU paging counter
and the VDU queue will be reset.

No entry parameters
On exit:
	X=0	No Escape condition found
	X<>0	The Escape condition cleared


A=&7F (127)	Check EOF status on open file
On entry:
	X=channel number
On exit:
	X=0	EOF not reached
	X<>0	EOF true


A=&80 (128)	Read ADC channel/Mouse coordinates/Buffer sizes

This call is used by Basic's ADVAL function and read the ADC channels, the
mouse coordinates and return the free space left in the system buffers.

(a) Read last ADC channel converted and fire buttons
On entry:
	X=0
On exit:
	Y=last channel converted
	X=contains fire button states in bits 0 and 1

(b) Read ADC channel
On entry:
	X=1	Read ADC channel 1
	X=2	Read ADC channel 2
	X=3	Read ADC channel 3
	X=4	Read ADC channel 4
	X=5
	X=6
On exit:
	YX=ADC value read

(c) Read mouse coordinates
On entry:
	X=7	Return X position of mouse
	X=8	Return Y position of mouse
On exit:
	YX=mouse coordinate

(d) Read buffer free space
On entry:
	X=&FF (-1)	Keyboard buffer
	X=&FE (-2)	RS232 input buffer
	X=&FD (-3)	RS232 output buffer
	X=&FC (-4)	Printer buffer
	X=&FB (-5)	Sound channel 0
	X=&FA (-6)	Sound channel 1
	X=&F9 (-7)	Sound channel 2
	X=&F8 (-8)	Sound channel 3
	X=&F7 (-9)	Speech buffer
	X=&F6 (-10)	Mouse buffer
On exit:
	YX=number of bytes free in buffer


A=&81 (129)	Read Key or Machine Type

This call is used by Basic's INKEY function and can be used to get a
character from the keyboard within a time limit, scan the keyboard for a
particular character or return information about the machine type.

(a)  Read key with time limit
On entry:
	XY<&8000	time limit in centiseconds
On exit:
	If character detected, X=ASCII value of key, Y=&00 and Cy=0
	If no character detected, Y=&FF, Cy=1 (X=&00)
	If ESCAPE pressed, Y=&1B (27), Cy=1 (X=&00)

(b)  Scan for key
On entry:
	X=negative INKEY value of key
	Y=&FF
On exit:
	X and Y contain &FF if the key is being pressed

(c)  Information on machine type
On entry:
	X=&00
	Y=&FF
On exit:
	X holds a value indicating the machine type: 
	X=&FF	-1	BBC Microcomputer (OS 1.00/1.20)
	X=&FE	254	American BBC Microcomputer
	X=&FD	253	Master 128
	X=&FC	252	West German BBC Microcomputer
	X=&FB	251	BBC B+
	X=&FA	250	Acorn Business Computer
	X=&F9	249
	X=&F8	248
	X=&F7	247	Master ET
	X=&F6	246
	X=&F5	245	Master Compact
	X=&F4	244
	X=&F3	243
	X=&F2	242
	X=&F1	241
	X=&F0	240

	X=&Ax		Archimedes:
	X=&A5	165	Archimedes RISC OS 3.5x
	X=&A4	164	Archimedes RISC OS 3.1x
	X=&A3	163	Archimedes RISC OS 3.0x
	X=&A2	162	Archimedes RISC OS 2.01
	X=&A1	161	Archimedes RISC OS 2.00
	X=&A0	160	Archimedes Arthur OS

	X=&01	1	Electron
	X=&00	0	BBC Microcomputer, (OS 0.10)

A=&82 (130)	Read machine high order address	

This call provides the top 16 bit high order address of the environment
the program is running in.

No entry parameters
On exit:
	YX contains the high order address:
	YX=&FFFF	Running in i/o processor
	YX<&FF00	Running in co-processor

A=&83 (131)	Return OSHWM (lowest address of user memory)

This call returns the address of the first byte in memory not used by the
operating system and so available as user memory.  It is used by Basic to
initialise PAGE.

No entry parameters
On exit:
	YX contains address of first byte of user memory


A=&84 (132)	Return top of user memory

This call returns the address of the first byte in memory not available
for the user.  It is used by Basic to initialise HIMEM.

No entry parameters
On exit:
	YX contains address of byte after end of user memory


A=&85 (133)	Return address of top of user memory for given mode

This call returns the address of the top of user memory in the i/o
processor if the given mode was changed to.

On entry:
	X=screen mode number
On exit:
	YX=address of top of user memory in i/o processor for given mode


A=&86 (134)	Read input cursor position

This is used by Basic to return the cursor position in POS and VPOS. 
During text editing, the input cursor position is returned.

No entry parameters
On exit:
	X=X coordinate
	Y=Y coordinate


A=&87 (135)	Read character at cursor position and screen mode
No entry parameters
On exit:
	X=character value or 0 if unrecognised
	Y=screen mode number (0-127, ignoring shadow state)


A=&88 (136)	Perform *CODE

This call is performed by the *CODE command and passes the parameters to
USERV with A=0.

On entry:
	X,Y are passed on to the USERV routine
On exit:
	X,Y contain the values returned from the USERV routine.







A=&89 (137)	Perform *MOTOR

This call is performed by the *MOTOR command and switches the cassette
motor relay (if present) on and off.

On entry:
	X=0	Relay off
	X<>0	Relay on
	Y	Ignored.  CFS sets Y=0 for reads and Y=1 for writes.

On exit:
	X,Y corrupted


A=&8A (138)