
Advantech SOM-ETX Design Guide
5.1.2.5 SOM-ETX PCI interface supply voltage
SOM-ETX PCI interface is 3.3V signaling environment but have 5V tolerance of I/O
signals. If a universal PCI connector be used at carried board, a jumper design to
select Vio for 5V and 3.3V is necessary. Otherwise, the suitable Vio voltage should
be designed for 5V or 3.3V connector.
Table 5.5 Add-in Card Supplied Power Selection
Symbol
3.3V Connector
5V Connector
Universal Connector
Vio 3.3V
5V
Jumper
select
Note:
1. Notice the riser card supply voltage type and do not plug in the wrong
supply voltage type connector. If the universal connector be used , make
sure the Vio jumper setting is correct when plug in the riser card.
2. Advantech demo carried board provides the 5V connector and 5V Vio for
PCI slots. Plug in a 3.3V riser card in wrong direction will cause the carried
board or riser card damage.
5.1.3 Layout Guidelines
The following represents a summary of the routing guidelines for the PCI devices.
Simulations assume that PCI cards follow the PCI Local Bus Specification, Revision
2.2, 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-
ETX
Connector X1
1
2
3
4
R_IDSEL
R_IDSEL
R_IDSEL
R_IDSEL
AD BUS
L1
L2
L3
L4
AD BUS
AD BUS
AD BUS
PCI AD Bus should be routed as daisy chain to PCI expanseion slots
W1
W1
W1
W1
W2
W2
W2
W2
Figure 5-3 PCI Bus Layout Example with IDSEL
Chapter 5 Carrier Board Design Guidelines
65
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