Ampro Corporation 486E - Manual (Page 78)

Little Board™/486e Technical Manual
2–62
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. Pins from both headers extend
through the board, providing male connections for PC/104-compliant peripherals or other devices.
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 36-pin edge card connector of a conventional ISA expansion bus. It has extra ground
positions at each end of the connector (C0, D0, and D19). (C19 is a key pin.) The extra grounds C0
and D0 are numbered “0” to keep the pin numbers of the remaining signals on the connector the
same as those on the standard ISA bus. 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/486e expansion bus.
The buffered output signals to the expansion bus are standard TTL level signals. All inputs to the
Little Board/486e CPU 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 Table
2–46 through Table 2–49, and indicate how the signals are terminated on the Little Board/486e
CPU.