PCI card - finding the voltages used

1. Introduction

The design of the PCI bus places a number of voltages in the bus connector. A PCI card may use one, multiple or all of the voltages provided . As a minimum all of the PCI cards use +3.3V and/or +5V power.
Depending on the functions of the card and the way they are realized, the PCI card may use other voltages as well.

This article will give you a practical way of recognizing what voltages a PCI card is using and what is necessary to make the PCI card function on one of the SSI2, or XPRS families of cards.

2. Voltages on the PCI bus

There are the four voltages provided for use on the PCI bus: +3.3V , +5V , +12V , -12V. The maximum currents defined in the speck are: +3.3V/7.6A , +5V/5A , +12V/500mA , -12V/100mA. Full details on the PCI bus are available on - Wikipedia, .

 

The PCI bus defines 'component' side of the PCI card as - side B (the above image), and 'solder' side - as side A (image below).



The specification defines 'keying' - openings on the bus side of the pc board. Based on the location of the openings, there are 3 types of boards: '5V card', '3.3V card', and 'universal (3.3V and 5v) card'.

The 2 images show 3 PCI cards, each one is 32bit, and one of them is '5V card', and the other 2 are - 'universal (3.3V and 5V) cards'.

Regardless of the 'keying' of a card, it may use both 3.3V and 5V voltages, even when defined as a 3.3V or 5V type of a card.

The power supplying pins for the optional +12V and -12V voltages are located on:

• side B - starting from the left to right: pin1 = -12V, pin2 = ........, pin3 = ...
• side A - starting from the right to left: pin1 = ......., pin2 = +12V, pin3 = ...
  
  There are the following scenarios for powering -
  - use 'pwr-5v' - PCI card-s using only 3.3/5v
  - or, use 'pwr-5v' and 'isa-pwr' - PCI card-s using 3.3/5v, and +12v,-12v low current
  - or, use 'isa-pwr-xr' - PCI card-s using 3.3/5v, and +12v,-12v high current
  
  

  3. Examples

  3.1. PCI card - need of +12V and -12V

  The PCI card in the picture below needs both optional voltages.
  
   
  
  Going through the pins reveals that - sideB/pin1=-12V (left image), and sideA/pin2=+12V (right image) are both connected/used. There are thick lines going up to the components on the circuit board .
  
  Based on the currents consumed by the PCI card on +12V, -12V, you can order and use:
  - pwr-5v (5V power supply) and isa-pwr (power supply module) if the consumed currents are less than 50ma
  - or, isa-pwr-xr (external power supply 25W) if the consumed currents are higher, or if unsure on the consumed currents
  
  

  3.2. PCI cards - no need of additional voltages

  The PCI cards in the pictures below do not need the optional voltages.
  
   
  
  The PCI card above is 'keyed' as a '5V card', as seen at the above images. The PCI card below is 'keyed' as a 'universal (3.3V and 5V) card', as seen at the images below.
  
   
  
  The 2 PCI cards above have all the pads, as seen at the 2 above images. The PCI cards below do not have all the pads, as seen at the image below.
  
   
  
  Going through the pins reveals that - sideB/pin1=-12V (left image), and sideA/pin2=+12V (right image) are both missing. There are no thick lines going up to the components on the circuit board .
  
  This PCI card uses only 3.3V & +5V, does need an additional 5V power supply - pwr-5v .
  
  

  3.3. PCI - need of +12V

  The PCI card in the pictures below need only one of the optional voltages.
  
   
  
  Going through the pins reveals that sideB/pin1=-12V (left image) is not connected/used. However sideA/pin2=+12V (right image) is connected/used - there is a thick line going up to the components on the circuit board .
  
  Based on the currents consumed by the PCI card on +12V, -12V you can order and use:
  - pwr-5v (5V power supply) and isa-pwr (power supply module) if the consumed currents are less than 50ma
  - or, isa-pwr-xr (external power supply 25W) if the consumed currents are higher, or if unsure on the consumed currents