Switching Serial Power On and Off
The serial I/O subsystem of the Macintosh Portable computer includes the
following components:
• the Serial Communications Controller (SCC) chip
• the serial driver chips
• the -5 volt supply
• the internal modem (if installed)
Because serial drivers always use these components in certain combinations,
the Power Manager provides five serial power procedures that perform the following tasks:
• The AOn procedure switches on power to serial port A and switches on power to the internal modem if it is installed.
(the modem port) but does not switch on power to the internal modem.
• The BOn procedure switches on power to serial port B. • The AOff procedure switches off power to serial port A and to the internal modem if it is in use.
• The BOff procedure switches off power to serial port B. If no internal modem is installed, then calling any of the power-on routines
switches on power to the SCC, the serial driver chips, and the -5 volt supply.
To switch power on for port B whether or not there is an internal modem
installed, use the BOn procedure. This procedure switches on power to the SCC, the serial driver chips, and the -5 volt supply.
If the internal modem is installed, then you can use the AOn procedure to switch on the modem. In this case, this procedure switches on power to the
SCC, the -5 volt supply, and the modem; the internal modem does not use the
serial driver chips.
If the internal modem is installed but you do not want to use it (whether or
not the user has used the Portable control panel to disconnect the modem), then
use the AOnIgnoreModem procedure to switch on power to the SCC, the serial driver chips, and the -5 volt supply.