This chapter describes miscellaneous VME chassis information. It contains the following sections:
“VME Chassis Description” describes VME chassis physical characteristics and slot designations.
“VME Chassis Power Supply Specifications” describes VME chassis power supply specifications.
“VME Chassis Grounding Information” describes VME chassis grounding perimeters.
The VME option uses three different-size chassis configurations from ELMA Electronics (6U/21-slot, 6U/5-slot, and 9U/5-slot). These chassis have special EMI and grounding standards that meet Silicon Graphics requirements and must be used for proper VME operation. (For ordering information, see Chapter 1.) Figure 3-1, Figure 3-2, and Figure 3-3 show the VME chassis slot locations.
 | Caution: The Silicon Graphics VME interface board is designed in compliance with standard ELMA/VME mechanical specifications. It is also designed to meet FCC Class A regulations when installed in an Silicon Graphics approved chassis in which all slots are filled either with shielded blank panels or with VME boards that include shielded front panels. |
If your VME boards are not compliant with ELMA/VME mechanical specifications, VME board problems can occur. The VME interface board has a row of grounding fingers adhered to the side of the front panel that provide EMI shielding. In some cases, adjacent IC leads from non-compliant ELMA/VME boards can contact these grounding fingers and cause the VME board to short out.
Therefore, it is recommended that you observe the following precautions when installing non-compliant ELMA/VME boards. With the system turned off, install a VME board in VME chassis slot 2 and visually inspect it to ensure that it is not contacting the VME interface board grounding fingers. If the adjacent VME board is contacting the grounding fingers, one of the following options will resolve the problem. (Note that these options apply only to systems where EMI shielding is not required.)
Remove the VME board from the VME chassis slot 2 and always leave slot 2 empty.
Cover the VME interface board grounding fingers with a non-conductive, protective tape.
Remove the grounding fingers from the VME interface board.
It is recommended that the Silicon Graphics VME interface board be used only with other ELMA/VME-compliant boards. The customer assumes full responsibility for all non-compliant ELMA/VME boards installed in the system. Silicon Graphics is not liable for any system problems that occur as a result of using non-compliant ELMA/VME boards.
This VME chassis holds a maximum of twenty 6U VME boards, plus one VME interface board (see Figure 3-1).
This VME chassis holds a maximum of four 6U VME boards, plus one VME interface board (see Figure 3-2).
This VME chassis holds a maximum of four 9U VME boards, plus one VME interface board (see Figure 3-3).
Table 3-1 describes the VME chassis power supply specifications.
Table 3-1. VME Chassis Power Supply Specifications
Chassis Type | Maximum Total Power Supply | Maximum Individual Supply Current |
|
|
|
|---|---|---|---|---|---|
|
| +5 V | +12 V | -5 V | -12 V |
9U/5-slot | 350 W | 50 A | 8 A | 4 A | 3 A |
6U/5-slot | 250 W | 40 A | 6 A | 2.5 A | 2.5 A |
6U/21-slot | 750 W | 120 A | 12 A | 8 A | 8 A |
Grounding issues are very important in the Origin family and Onyx2 systems. Each Silicon Graphics system chassis must be well grounded through its power connector. All chassis connected with XIO copper cables must share the same transformer, must be well grounded through the same earthing rod, and must be on the same branch circuit. If you have any doubts about the quality of the ground connection, it is important that you consult with a qualified electrician. A grounding cable connected between the VME enclosure(s) and the host XIO connection eliminates any problems related to common grounding.
Note that the grounding lugs on the VME option board and the VME XIO board must be connected using the VME grounding cable. If needed, the grounding lug on the VME enclosure is used to ground the VME chassis to the rack.
| Caution: Any difference in ground potential greater than 500 millivolts (0.5 volts) between two chassis connected by copper XIO cables can cause severe equipment damage, and can create hazardous conditions. |
The branch circuit wiring should be provided with an insulated grounding conductor that is identical in size, insulation material, and thickness to the earthed and unearthed branch-circuit supply conductors.
The grounding conductor should be green, with or without one or more yellow stripes. This grounding or earthing conductor should be connected to earth at the service equipment or, if supplied by a separately derived system, at the supply transformer or motor-generated set.
The power receptacles in the vicinity of the systems should all be of an earthing type, and the grounding or earthing conductors serving these receptacles should be connected to earth at the service equipment.