Specifications

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Because both of these critical circuits are fully digital, the floppy drive interface is highly reliable
and temperature independent.
The board's ROM-BIOS initializes the floppy subsystem configuration based on data stored within
the board's Configuration Memory (in the battery-backed CMOS RAM within the clock device).
All combinations of supported drives can be used (see Chapter 2).
Interrupt channel 6 and DMA channel 2 are used for normal operation of the floppy controller
subsystem. If the floppy controller option is not present, these resources -- and also the floppy
controller's I/O port addresses -- are available on the AT Expansion Bus. In fact, a floppy
controller card on the AT Expansion Bus could be substituted, provided the onboard floppy
controller option is not present.
Refer to Chapter 2 for jumpering information and for the port's connector pinout.
4.5 SERIAL/PARALLEL CONTROLLER
A single high integration component (U22) provides two AT (and PC) compatible serial ports, and
an AT (and PC) compatible parallel printer port as well. These devices are identical in
functionality with the normal serial and parallel controllers of standard AT's, with on exception:
the Little Board/286 parallel port has bidirectional data lines.
4.5.1 Serial Ports
The 16C452 device contains two 8250 (16C450) compatible serial controllers. As is the case
with standard PC and AT compatible serial controllers, these devices provide two full duplex
asynchronous communications channels with software selectable baud rates (up to 57.6K baud),
word size (5-8 bits), and stop bits (1, 1.5, or 2).
Each of the two serial ports is equipped with three output and 5 input signals (as in the standard
AT). Signals are buffered with EIA compatible RS232C buffers (U15 and U16). U16 is used for
the primary serial channel, while U15 is for the secondary serial channel. Although the Little
Board/286 operates from a single +5 volt power supply, +12 and -12 VDC voltages for operation
of the RS232C drivers are generated by means of onboard DC-to-DC converters. The -12V power
is generated within the RS232C driver devices themselves, while the +12V power is generated by
a separate power converter circuit (U8).
Either or both serial ports can be hardware disabled via configuration data within the board's
configuration EEPROM (under control of the board's ROM-BIOS). This is normally done using
the Ampro SETUP utility. When a port is disabled in this manner, its I/O port addresses and
system interrupt become available on the AT Expansion Bus for other devices in the system. For
example, an application might require that a modem or alternative serial communications card be
substituted for the primary serial device.
Each serial port's I/O connector includes a driver output enable signal (J3 pin 10) which is used for
factory test purposes only. This signal is pulled low on the board by a 1K resistor and should be
left unconnected.
Refer to Chapter 2 for information on the connector pinouts of these two ports.