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Advantech SOM-Express Design Guide
44
Chapter 5 Carrier Board Design Guidelines
5.1.2.5 SOM-Express PCI interface supply voltage
The SOM-Express PCI interface is a 3.3 V signaling environment but has 5 V
tolerance for I/O signals. If a universal PCI connector is used at the carrier board, a
jumper design to select Vio for 5 V and 3.3 V is necessary. Otherwise, the suitable
Vio voltage should be designed for a 5 V or 3.3 V connector.
Table 5.6 Add-in Card Supplied Power Selection
Symbol
3.3 V Connector
5 V Connector
Universal Connector
Vio
3.3 V
5 V
Jumper select
Note:
1. Note the riser card supply voltage and do not plug in the wrong supply
voltage. If a universal connector is used, make sure the Vio jumper setting
is correct when plugged into the riser card.
2. Advantech’s demo carrier board provides a 5 V connector and 5 V Vio for
PCI slots. Plugging a 3.3 V riser card in the wrong direction will cause
carrier board or riser card damage.
5.1.3 Layout Guidelines
The following represents a summary of the routing guidelines for PCI devices.
Simulations assume that PCI cards follow the PCI Local Bus Specification, Revision
2.3, trace length guidelines.
5.1.3.1 PCI Bus Layout Example with IDSEL
The following guidelines apply to platforms with nominal impedances of 55
Ω
± 10%.
SOM-
Express
Connector
0
1
2
3
R_IDSEL
R_IDSEL
R_IDSEL
R_IDSEL
W1
W2
AD BUS
L1
L2
L3
L4
W1
W2
W2
W2
W1
W1
AD BUS
AD BUS
AD BUS
PCI AD Bus should be routed as daisy chain to PCI expansion
slots
Figure 5-3 PCI Bus Layout Example with IDSEL
Содержание SOM-5780
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