@Database "AmigaFlight Binary Coded Decimal Instructions"
@$VER: AmigaFlight® Binary Guide 1.2 (17.02.94)
@Author Andrew Duffy & Chris Morris
@(c) 1992-1994, XCNT Productions

@Index "AmigaFlight:Help/Assembly/Assembly.guide/AssemblyIndex"}

@Tab=8

@Node Main "AmigaFlight® Help: Binary Coded Decimal Instructions"
@Toc "AmigaFlight:Help/Assembly/Assembly.guide/InstructSet"
Binary Coded Decimal Instructions
=================================

There are  three operations on numbers in BCD, each of which  operates on a
byte only (two decimal digits) and incorporate the extend flag:


	@{"ABCD            " LINK "ABCD"}  Add Decimal with Extend
	@{"NBCD            " LINK "NBCD"}  Negate Decimal with Extend
	@{"SBCD            " LINK "SBCD"}  Subtract Decimal with Extend
@EndNode         

@Node ABCD "AmigaFlight® Help: Add Decimal with Extend"
ABCD	Add Decimal with Extend
===============================

	Add  the  source  operand to the  destination operand using Binary
	Coded   Decimal   (BCD)   arithmetic.  Store  the  result  in  the
	destination operand.

	Destn + Source + X  -> Destn


Assembler Syntax
----------------
	ABCD	Dy,Dx
	ABCD	-(Ay),-(Ax)


Data Size
---------
	Byte


Status Flags
------------
	N  Undefined
	Z  Clear if result non-zero else unchanged
	V  Undefined
	C  Set if carry (decimal) else clear
	X  Set same as carry


Instruction Size and Cycles to Execute
--------------------------------------
			#	p
	Dy,Dx		2	6
	-(Ay),-(Ax)	2	18

	# = no. of program bytes
	p = no. of instruction clock periods
@EndNode

@Node NBCD "AmigaFlight® Help: Negate Decimal with Extend"
NBCD	Negate Decimal with Extend
==================================

	Subtract the destination operand and the  source  operand  and the
	extend bit from zero, and store the result back in the destination
	location. This produces a tens complement if  the extend bit is 0,
	a nines complement if it is set. This is a byte operation only.

	0 - Destn - X -> Destn


Assembler Syntax
----------------
	NBCD	<ea>

	<ea> - data alterable


Addressing Modes
----------------
	Mode				     Source  Destination
	
	Data Register Direct			-	*
	Address Register Direct			-	-
	Address Register Indirect		-	*
	Postincrement Register Indirect		-	*
	Predecrement Register Indirect		-	*
	Register Indirect with Offset		-	*
	Register Indirect with Index		-	*
	Absolute Short				-	*
	Absolute Long				-	*
	P.C. Relative with Offset		-	-
	P.C. Relative with Index		-	-
	Immediate				-	-


Data Size
---------
	Byte


Status Flags
------------
	N  Undefined
	Z  Cleared if result non-zero, else unchanged
	V  Undefined
	C  Set if borrow (decimal), else cleared
	X  Set same as carry bit


Instruction Size and Cycles to Execute
--------------------------------------
	<ea>		#	p  
	Dn		2	6  
	(An)		2	12 
	(An)+		2	12 
	-(An)		2	14 
	d16(An)		4	16 
	d8(An,Ri)	4	18 
	Abs short	4	16 
	Abs long	6	20 

	# = no. of program bytes
	p = no. of instruction clock periods
@EndNode

@Node SBCD "AmigaFlight® Help: Subtract Decimal with Extend"
SBCD	Subtract Decimal with Extend
====================================

	Subtract the  source  operand  from the destination  operand using
	binary  coded  decimal  (BCD) arithmetic. Store the  result in the
	destination operand.

	Destn - Source - X  -> Destn


Assembler Syntax
----------------
	SBCD	Dy,Dx
	SBCD	-(Ay),-(Ax)


Data Size
---------
	Byte


Status Flags
------------
	N  Undefined
	Z  Clear if result <> 0 else unchanged
	V  Undefined
	C  Set if borrow (decimal) else clear
	X  Set same as carry


Instruction Size and Cycles to Execute
--------------------------------------
			#	p
	Dy,Dx		2	6
	-(Ay),-(Ax)	2	18

	# = no. of program bytes
	p = no. of instruction clock periods
@Endnode