Specifications

Software Configuration
3–37
A complete description of the PC Video interface is beyond the scope of this manual. To find out more
about the PC Video interface, its timing and architecture, contact:
Chips and Technologies
2950 Zanker Road
San Jose, CA 95134
Phone: [phone]
Telex: 272929 CHIPS UR
FAX: [phone]
Ask for information pertinent to the 65545 High Performance Flat Panel/CRT VGA controller and its use
with “PC Video”.
3.15 PC SPEAKER
One of the core control logic devices includes a standard AT-compatible speaker port. The speaker logic
signal is buffered by a transistor amplifier, and provides about 100 milliwatts to an external 8 ohm
speaker.
The audio output is based on two signals: the output of Timer 2; and the programming of two bits, 0 and
1, at I/O port 61h. Bit 1 of I/O port 61h is one term of a 2-input AND gate. The other term is the output
from Timer 2. Thus, setting bit 1 to a logic 1 enables the output of Timer 2 to the speaker, and a logic 0
disables it. If you disable Timer 2 by setting bit 0 of port 61h to a 0, then you can use bit 1 of port 61h to
control the speaker directly.
3.16 WATCHDOG TIMER
The purpose of a watchdog timer function is to restart the system should some mishap occur. Possible
problems include: a failure to boot properly; the application software losing control; temporary power
supply problems including spikes, surges, or interference; the failure of an interface device; unexpected
conditions on the bus; or other hardware or software malfunctions. The watchdog timer helps assure
proper start-up after an interruption.
The Little Board/486i ROM-BIOS supports the board’s watchdog timer function in two ways:
! There is an initial watchdog timer setting, specified using SETUP, which determines whether the
watchdog timer will be used to monitor the system boot, and if so, how long the time-out is (30, 60, or
90 seconds).
! There is a special ROM-BIOS function which may be used by application software to start, stop, and
retrigger the watchdog timer function.
The initial time-out should be set (using SETUP) to be long enough to guarantee that the system can boot
and pass control to the application. Then, the application must periodically retrigger the timer so that the
time-out does not occur. If the time-out does occur, the system will respond in a manner determined by
how the watchdog timer jumper, W11, is set (see Chapter 2).
The following simple assembly language routine illustrates how to control the watchdog timer using the
Ampro ROM-BIOS function that has been provided for this purpose: