Specifications

Hardware Configuration
2–45
2.17 AT EXPANSION BUS
The PC/AT expansion bus appears on a pair of header connectors at P1 and P2. P1 is a 64-pin female
dual-row header. P2 is a 40-pin female dual-row header. The PC-bus subset of the expansion bus
connects to the first 62 positions of P1; the two additional positions of P1 (A32 and B32) are added
grounds to enhance system reliability. Connector P2 replaces the 32-pin edgecard connector of a
conventional AT expansion bus. It has extra ground positions at each end of the connector (C0, D0,
D19). (C19 is a key pin.) The layout of signals on P1 and P2 is compliant with the PC/104 bus
specification. PC/104-compatible expansion modules can be installed on the Little Board/486i
expansion bus.
The buffered output signals to the expansion bus are standard TTL level signals. All inputs to the
Little Board/486i operate at TTL levels and present a typical CMOS load to the expansion bus. The
current ratings for most output signals driving the AT expansion bus are shown in Tables 2-35
through 2-38, and indicate how the signals are terminated on the Little Board/486i.
2.17.1 On-board MiniModule Expansion
You can install one or more Ampro MiniModule products or other PC/104 modules on the Little
Board/486i expansion connectors. When installed on P1 and P2, the expansion modules fit within the
Little Board/486i’s outline dimensions. Most Ampro MiniModule products have stackthrough
connectors compatible with the PC/104 Version 2.1 specification. You can stack several modules on
the Little Board/486i headers. Each additional module increases the thickness of the package by 0.66
inches (17 mm). See Figure 2-15.
Figure 2-16 Stacking PC/104 Modules on the Little Board/486i
2.17.2 Using Standard PC and AT Bus Cards
Ampro offers several options that allow you to add conventional 8-bit and 16-bit ISA expansion cards
to the Little Board/486i system. Contact Ampro for further information about optional bus expansion
products.