Switchable Devices; Communications And The Bios Automatic Power Saving Features - Husky MP2500 Manual

32.3.3 Switchable devices

There are several devices which consume significant power, that you can
control from programs. You should keep their use to a minimum:
•
The backlight option. Use INT 10H function 65H to set a timeout and
INT 10H function 78H to turn it on and off.
•
The RS232 interface. This turns on automatically when needed, but
programs should turn it off when not needed, using INT 14H function
25H.
32.3.4 Communications and the BIOS Automatic
Power Saving Features
Any access to the serial communications port (COM2) will cause the BIOS
to use HALT mode rather than STOP mode. Although this will result in
lower ongoing power usage it will keep the processor active in order to be
prepared to receive incoming interrupts and consequently prevent time-outs
from being used correctly.
To re-enable STOP mode after communications is complete the application
should follow these steps:
• The handshaking lines (RTS and DTR) should be deactivated and any
response from the other end waited for. This should ensure that the
other end knows that communications has finished.
• The receive and transmit buffers should be flushed and the
communications shut down (UART interrupts disabled, service routines
revectored etc. as appropriate). This will prevent further interrupts and
other comms activity from causing the BIOS to go back into HALT
mode.
• The communications receive buffer should be emptied.
• The RS232 driver should be turned off using INT 14H function AH=25h,
AL=0 and DX=1 (Chapter 25). (The driver is automatically reactivated
whenever the UART is accessed.)
• Finally, the application should re-enable STOP mode as described in the
previous section.
Chapter 32: Using Power Handling 309