xMachine command summary

Modified from Eck: The Most Complex Machine

Basic Instructions

Some of these instructions (NOT, SHL, SHR, INC, DEC, HLT) take no parameter. If a parameter is present, it will be ignored. The operation will be performed on the accumulator. The other commands in this table take a cell address as a parameter. The operation will always involve the accumulator and the contents of the cell address given. The results will be placed back in the accumulator. All the basic instructions begin with 00

Code	Nickname	Name	Example	Description
000000	ADD	Add-to-AC	ADD 12	Adds contents of address 12 to accumulator
000001	SUB	Subtract-from-AC	SUB 12	Subtracts contents of address 12 from accumulator
000010	AND	Logical-AND-with-AC	AND 12	Performs bitwise AND with contents of address 12
000011	OR	Logical-OR-with-AC	OR 12	Performs bitwise OR with contents of address 12
000100	NOT	Logical-NOT-of-AC	NOT	Performs complement (bitwise NOT) of accumulator Parameter ignored
000101	SHL	Shift-AC-left	SHL	Shifts each digit of accumulator one digit left multiplies accumulator by two
000110	SHR	Shift-AC-right	SHR	Shifts each digit of accumulator one digit right divides accumulator by two
000111	INC	Increment-AC	INC	Adds one to accumulator
001000	DEC	Decrement-AC	DEC	Subtracts one from accumulator
001001	LOD	LOD-AC-from-memory	LOD 12	Copies the value from address 12 to accumulator
001010	STO	STO-AC-in-memory	STO 12	Stores the value in accumulator to address 12
001011	HLT	Halt	HLT	Stops program execution
001100	JMP	Jump	JMP 12	Transfers program control to instruction in address 12
001101	JMZ	Jump-if-AC-is-zero	JMZ 12	If accumulator is zero, jump to instruction in address 12 Otherwise, move on to next instruction
001110	JMN	Jump-if-AC-is-negative	JMN 12	If accumulator is negative, jump to instruction in address 12 Otherwise, move on to next instruction
001111	JMF	Jump-if-FLAG-is-set	JMF 12	If FLAG register is on, jump to instruction in address 12 Otherwise, move on to next instruction

Constant addressing instructions

The constant addressing commands all take a number as a parameter. This actual value is manipulated with the accumulator. All the constant addressed instructions begin with 01.

Code	Nickname	Name	Example	Description
010000	ADD-C	Add-Constant-to-AC	ADD-C 12	Adds value 12 to accumulator
010001	SUB-C	Subtract-Constant-from-AC	SUB-C 12	Subtracts value 12 from accumulator
010010	AND-C	Logical-AND-Constant-with-AC	AND-C 12	Performs bitwise AND with value 12
010011	OR-C	Logical-OR-Constant-with-AC	OR-C 12	Performs bitwise OR with value 12
011001	LOD-C	LOD-AC-with-Constant	LOD-C 12	Copies the value 12 to accumulator

Indirect Addressing Instructions

The indirect addressing functions add tremendous flexibility to the system. The parameter of the command is an address, but that address does not hold the actual data, but another address, which does hold the data. So, if address 12 contains the value 20, and address 20 contains the value 50, the command STO-I 12 looks at cell 12 to get an address (20). It then looks in cell 20 to get the actual value (50), and stores the value 50 in the accumulator. The advantage of this approach is that a routine can be devised to manipulate multiple address cells within loops. This is useful for manipulating text data or arrays of variables. All indirect addressing commands begin with 10.

Code	Nickname	Name	Example	Description
100000	ADD-I	Add-Indirect-to-AC	ADD-I 12	Adds contents of address referred by 12 to accumulator
100001	SUB-I	Subtract-from-AC	SUB-I 12	Subtracts contents of address referred by 12 from accumulator
100010	AND-I	Logical-AND-Indirect-with-AC	AND-I 12	Performs bitwise AND with contents of address referred by 12
100011	OR-I	Logical-OR-Indirect-with-AC	OR-I 12	Performs bitwise OR with contents of address referred by 12
101001	LOD-I	LOD-AC-Indirect-from-memory	LOD-I 12	Copies the value from address referred by 12 to accumulator
101010	STO-I	STO-AC-Indirect-in-memory	STO-I 12	Stores the value in accumulator to address referred by 12
101100	JMP-I	Jump-Indirect	JMP-I 12	Transfers program control to instruction in address referred by 12
101101	JMZ-I	Jump-Indirect-if-AC-is-zero	JMZ-I 12	If accumulator is zero, jump to instruction in address referred by 12 Otherwise, move on to next instruction
101110	JMN-I	Jump-Indirect-if-AC-is-negative	JMN-I 12	If accumulator is negative, jump to instruction in address referred by 12. Otherwise, move on to next instruction
101111	JMF-I	Jump-Indirect-if-FLAG-is-set	JMF-I 12	If FLAG register is on, jump to instruction in address referred by 12. Otherwise, move on to next instruction

© Andy Harris
Indiana University / Purdue University, Indianapolis
email: aharris@cs.iupui.edu
homepage: http://www.cs.iupui.edu/~aharris