Specifications

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2.6 AT EXPANSION BUS
An AT compatible expansion bus appears at connectors J9 and J10, except that it is brought out
to a pair of header connectors, rather than edgecard connectors.
The PC-bus subset of the board's AT Expansion Bus connects to the first 62 pins of J9; the two
additional pins of J9 (A32, B32) offer additional ground signals, for enhanced system reliability.
The 36-pin edgecard connector, normally included in an AT expansion bus, is replaced by a 40-
pin header connector, at J10. As with J9, additional ground connections have been provided. In
this case, there are two additional ground pins at each end of the connector. AT Expansion Bus
connector pinouts are given later in this chapter.
Table 2-18 shows the pinout and signal functions of the signals on the board's AT Expansion Bus
and MiniModule headers. Further information about these signals is available in numerous
publications, including the IBM technical reference manuals for the PC and AT computers, and
from the reference documents listed in the beginning of Chapter 4.
Note that the board's AT Expansion Bus and MiniModule connector pins are numbered differently
from the other header connectors on the board, so that they correspond to the scheme normally
used on the PC and AT Expansion Bus. Specifically, rather than being designated numerically
(1, 2, 3, etc.) the signals of the AT Expansion Bus are designated alpha-numerically (A1, A2, ...,
B1, B2, ..., etc).
With the exception of the onboard serial, parallel, and floppy controllers, all signal outputs
driving the AT Expansion Bus are rated at 24 mA sink current at a logic "low" level of 0.4 Volts.
(The serial and parallel controllers provide 16 mA bus drive, and the floppy controller provides 12
mA.)
Note
Most PC and AT bus plug-in cards are intended for use on
an 8 MHz bus. It is therefore advisable to use one of the
Ampro utilities (SETUP or SETSPEED) to enable the board's
AT expansion bus "half-speed" option when PC or AT bus
plug-in cards are to be used, unless the cards are known to
operate properly at the faster bus speed of the Little
Board/286.
2.6.1 Onboard MiniModule Header and Bus Expansion
An important feature of the Little Board/286 is its onboard MiniModule headers. Two header
connectors, J9 and J10, provide an AT Expansion Bus interface for use with one of Ampro's 3.6"
x 3.8" expansion MiniModules. When installed on J9 (PC bus subset of the AT expansion bus),
the onboard expansion module fits within the Little Board/286's space envelope. The onboard
expansion module provides a bus pass-through connector, allowing additional external bus
expansion when the module is installed.