OSBYTE

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OSBYTE performs various functions passing and returning up to two bytes of data.

Specification

6502 Z80 6809 PDP11 80x86 32016 ARM 68000 RISC-V On entry: On exit:
A A A R0 AL R1 R0 D0 A0 = function code   preserved, but see &83 and &84.
X L X R1 BX R2 R1 D1 A1 = first parameter returned value
Y H Y R2 CX R3 R2 D2 A2 = second parameter if A>&7F, ignored and forced to &00 if A<&80   returned value if A>&7F
Cy Cy Cy Cy Cy Cy Cy Cy Cy returned value if A>&7F

Calling from BBC BASIC

Entry points

  • BBC BASIC Entry Address: &FFF4
  • 6502 Entry Address: &FFF4, vectors via &020A
  • Z80 Entry Address: &FFF4, vectors via &FFF5
  • 6809 Entry Address: &FFF4, vectors via &FFF5
  • 80x86 Entry Address: INT &4B, vectors via 0000:012C
  • 32000 Entry Address: SVC &06
  • PDP11 Entry Address: EMT 2
  • ARM Entry Address: SWI &06 "OS_Byte", vector &06
  • 68000 Entry Address: MOV #&06,A0:TRAP 12
  • RISC-V Entry Address: ECALL &AC0002

Implementations

Any OSBYTE call not recognised by the operating system is passed to sideways ROMs. If no sideways ROM recognises the call, then X is returned set to &FF.

The *FX command calls OSBYTE and generates the Bad command error if it is not recognised.

See also

Jgharston 16:58, 6 November 2009 (UTC)