user manual

2-3

Power Budget

Power Budgeting

If your workstation’s application requires several accessory cards and mass

storage devices, power budgeting may be required. Power budgeting ensures

that the power needed for the following internal devices does not exceed the

power available:

• Mass storage devices

• Model 743 and Model 744 VMEbus Board Computer(s)

• Standard internal printed circuit boards

• VME, PCI, and EISA accessory cards

The Model 748 ruggedized workstation uses two power supplies. Each

power supply provides voltages to the workstation's modules and accessory

card slots as listed in Table 2-6 and Table 2-7.

These tables are also worksheets to use in determining your power budget.

You may photocopy these tables as needed.

To determine the workstation’s power needs, follow these instructions:

1 Determine the board computer’s current requirements from the Computer

Current Requirements Worksheet (Table 2-3 or Table 2-4).

2 To determine the maximum current usage of the Model 744 memory

cards, either use Figure 2-1 and Table 2-1 (for Model 744/132L) or Table

2-2 (for Model 744/165L). You must work with the worst case power

draw to correctly determine power usage. Determine worst case power

draw by examining active memory bank configurations, using the follow-

ing steps:

a Examine your memory card configuration, noting which size card is in

each memory slot.

b The worst case active memory bank configuration depends on the slot position of the

memory cards, and the size of the cards. The 32 MB memory card has two banks per

card, and the 16, 64,128, and 256 MB cards each have only one memory bank per card.

• When 32 MB cards are used as a pair in memory slots 2 and 3 they can use three

memory banks concurrently.

• When used as a pair in slots 0, 1, or 2, the 32 MB cards can have two active mem-