Specifications

PCIe/104 and PCI/104-Express Specification Revision 3.0 February 17, 2015 Page 32
4. PCIe/104 Type 1 and Type 2 Stacking
4.1. System Stacking Rules
These rules will insure that the systems are not damaged when different type peripheral boards and host modules are
stacked together. A 1-bank implementation is limited to the PCI Express x1and USB 2.0 features noted below; the STKx
signals are not present.
Table 4-1 Required Host State When Peripherals Are Placed on Type 1 and Type 2 Hosts
Peripheral Card Type 1 Host Configuration
Type 2 Host
Bus Used Type x16 x8 x4
Alternate
Function
Alternate Function 1 Reset Good Reset
PCI Express x16 1 Good Reset Reset
PCI Express x8 1 Good Reset Reset
PCI Express x4 Universal Good Reset Good
PCI Express x1 Universal Good Good
USB 2.0 Universal Good Good
USB 3.0 2 Reset Good
SATA 2 Reset Good
LPC 2 Reset Good
Table 4-2 Peripheral Effect on Type 1 Host CPU Signals
Bus
Peripheral 53 STK0/WAKE# 54 STK1/PEG_ENA# 105 STK2/SDVO_DAT
Type 1 PCIe x16 or x8 No Change 0 = Enable PCIe x16 No Change
Type 1 Alternate Function No Change No Change 1 = Enable GFX
Type 2 SATA, USB 3.0, LPC 0 = Bus Stacking Error No Change No Change
Universal PCIe x4 No Change 0 = Enable PCIe x16 No Change
Universal PCIe x1, USB 2.0 No Change No Change No Change
Table 4-3 Peripheral Effect on Type 2 Host CPU Signals
Bus Peripheral 53 STK0/WAKE# 54 STK1/PEG_ENA# 105 STK2/SDVO_DAT
Type 1 PCIe x16 or x8 No Change 0 = Bus Stacking Error No Change
Type 1 Alternate Function No Change No Change 1 = Bus Stacking Error
Type 2 SATA, USB 3.0, LPC 0 = Normal Operation No Change No Change
Universal PCIe x4 No Change 1 = Normal Operation No Change
Universal PCIe x1, USB 2.0 No Change No Change No Change
• The PCI Express signals may always be driven, but it is recommended that they are Hi-Z during reset.
• The system should provide some indication to the user when a bus stacking error has occurred, i.e. a blinking
LED.
• A PCI Express Link may only traverse up to six stacked PCI Express connector heights and all PCI Express
modules should be on the same side of the host if the top and bottom PCI Express connectors are electrically
connected together.
• A PCI Express Link may only be attached to a single connector on the Host.
• A PCI bus may only traverse up to four stacked PCI connectors, and they must all be on the same side of the
Host. Because of the requirements of trace length matching, all PCI Devices must be stacked together and must
be next to the Host
4.2. Host Configuration Rules
There are a set of rules to ensure that improper stacking does not damage either the host or peripheral boards. In addition
to connecting the pins as specified in Table 4-5, if a bus stacking error is detected the host shall hold the system in reset.
The host can optionally indicate to the user a stacking error.