microATX Motherboard Interface Specification

microATX Motherboard Interface Specification
Version 1.2
Page 4
Contents
1. Executive Summary.................................................................................. 6
1.1 Other Technical Documents ..................................................................................................6
1.2 microATX Form-factor Overview ...........................................................................................7
1.3 Benefits to Users ...................................................................................................................8
1.4 Benefits to Manufacturers......................................................................................................8
1.5 Mounting microATX Motherboard in an ATX Chassis ...........................................................8
2. Layout ........................................................................................................ 9
2.1 Board Dimensions .................................................................................................................9
2.2 Mounting Hole Placement......................................................................................................9
2.3 Connector Placement ............................................................................................................11
2.3.1 Expansion Slots .............................................................................................................11
2.3.2 Disk I/O 13
2.3.3 Front Panel I/O ..............................................................................................................13
2.3.4 Back Panel I/O...............................................................................................................13
2.3.5 Memory Sockets............................................................................................................16
2.3.6 Processor ......................................................................................................................16
2.3.7 Power Supply Connector ...............................................................................................16
2.4 Height Constraints .................................................................................................................17
2.4.1 Primary (Component) Side Height Constraints .............................................................17
2.4.2 Secondary (Bottom/Solder) Side Height Constraints.....................................................17
3. Power Supply Connector Information................................................... 19
3.1 Main Power Connector ..........................................................................................................19
3.2 Signal Control Definitions ......................................................................................................20
3.2.1 PS-ON 20
3.2.2 5VSB 20
3.2.3 Power Good Signal, PW-OK .........................................................................................20
3.3 Voltage Tolerances................................................................................................................21
3.4 Optional 6-pin Power Connector ...........................................................................................21
3.4.1 FanM Signal ..................................................................................................................22
3.4.2 FanC Signal...................................................................................................................22
3.4.3 3.3V Sense Line ............................................................................................................23
3.4.4 1394V Pin ......................................................................................................................23
3.4.5 1394R Pin......................................................................................................................23
Figures
1: Example of a microATX System............................................................................................7
2: microATX and ATX Form-factor Mounting Holes ..................................................................10
3: Example microATX Layout Diagram......................................................................................12
4: Chassis I/O Aperture Requirements ......................................................................................14
5: Motherboard I/O Connector Location Recommendation .......................................................15