Flags

RIX8 maintains two condition flags: Z (Zero) and C (Carry). They are stored in a flags register that is not directly readable or writable by software.

Flag Definitions

Flag	Bit	Name	Meaning
Z	0	Zero	Set when the result of an operation is 0x00
C	1	Carry	Set on carry-out (ADD) or borrow (SUB)

Instructions That Update Flags

Instruction	Updates Z	Updates C
ADD	Yes	Yes
ADDI	Yes	Yes
SUB	Yes	Yes
AND	Yes	No
OR	Yes	No
XOR	Yes	No
ANDI	Yes	No
ORI	Yes	No
SLL	Yes	Yes
SRL	Yes	Yes
LW	Yes	No
SW	No	No
BEQ	No	No
BNE	No	No
JAL	No	No
LDI	Yes	No

How Flags Are Used

In the current instruction set, branches (BEQ, BNE) compare two registers directly and do not consult the flags. The flags are maintained for future conditional instructions and for software that wishes to inspect them (though there is no instruction to read them directly).

Carry Semantics

• ADD / ADDI: C is set if the unsigned sum exceeds 0xFF.
• SUB: C is set if rs1 < rs2 (borrow occurred).
• SLL: C is set to the last bit shifted out.
• SRL: C is set to the last bit shifted out.

Zero Semantics

Z is set when the 8-bit result of the operation is 0x00. It is cleared otherwise.