SBA ISA
Developer	General Instrument
Implementation	SBA
Dev model	proprietary
Data word size	1 bit 0.125 octets 0.25 nibbles
Instruction word size	8 bit 1 octets
Instructions	24
Introduction	1977
Version	1
Format	stack
Endianness	bi-endian
Registers	0
ISAs • By Company • By Inst • By Data

The SBA ISA was an instruction set architecture used in the General Instrument's SBA family of 1-bit microcontrollers.

ISA

The SBA family had 8-bit instructions of two types: with immediate and without immediate value.

• With immediate: The 5 MSBs are reserved for the address, but only up to the 30th address. The opcode is stored in the 3 LSBs.

00000₂-11101₂000₂-111₂

• Without immediate: Addresses 30 and 31 are reserved for extended instructions of 8 bits.

11110000₂-11111111₂

This scheme allows for 30 addresses and 24 instructions (8 operating on immediate values and 16 without immediates).

Listing

SBA ISA
Mnemonic	Opcode	Action
ANDIN	AAAAA0002	In[AAAAA] · Stack[Top]
NANDIN	AAAAA0012	In[AAAAA] · Stack[Top]
ANDSS	AAAAA0102	Store[AAAAA] · Stack[Top]
NANDSS	AAAAA0112	Store[AAAAA] · Stack[Top]
ASP1	AAAAA1002	Store[AAAAA] · Stack[Top] ; PUSH(1)
NASP1	AAAAA1012	Store[AAAAA] · Stack[Top] ; PUSH(1)
STORE	AAAAA1102	Store[AAAAA] = Stack[Top] ; Stack[Top] = 1
OUTPUT	AAAAA1112	Out[AAAAA] = Stack[Top] ; Stack[Top] = 1
RESTART	111100002	restarts evaluation of program
INVERT	111100012	Stack[Top] = Stack[Top]
PAGE	111100102	Change page
HOME	111100112	Back to home page
PUSH0	111101002	PUSH(0)
PUSH1	111101012	PUSH(1)
PUSHC	111101102	PUSH(Stack[Top])
POP	111101112	POP()
AND	111110002	Stack[Top] = Stack[Top] · Stack[Top-1]
OR	111110012	Stack[Top] = Stack[Top] + Stack[Top-1]
EXOR	111110102	Stack[Top] = Stack[Top] ⊕ Stack[Top-1]
COMP	111110112
PAND	111111002	PUSH(Stack[Top] · Stack[Top-1]) ; Stack[Top] = 1
POR	111111012	PUSH(Stack[Top] + Stack[Top-1]) ; Stack[Top] = 1
PEXOR	111111102	PUSH(Stack[Top] ⊕ Stack[Top-1]) ; Stack[Top] = 1
PCOMP	111111112

See also

• 1-bit
• SBA