Ampro Corporation 486E manual AT Expansion Bus

Little Board™/486e Technical Manual

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.

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