SED

SED (short for "SEt Decimal flag") is the mnemonic for a machine language instruction which sets the decimal flag. It complements the CLD (clear decimal flag) instruction.

Addressing mode

Opcode		Addressing mode	Assembler format	Length in bytes	Number of cycles
Dec	Hex
248	F8	Implied	SED	1	2

SED only supports the Implied addressing mode, as shown in the table at right.

CPU flags

SED affects no processor status flags other than the decimal flag, which is always unconditionally set.

Examples

Convert a hex digit to PETSCII

Convert a hex digit in the accumulator ($00 to $0F) to PETSCII symbol "0" to "9" ($30 to $39) or "A" to "F" ($41 to $46)

SED
CMP #$0A ; sets carry if accumulator is $0A to $0F
ADC #$30 ; decimal mode add 30+carry = 30 or 31
CLD

Links

• NMOS 6510 Unintended Opcodes (No More Secrets)