Section 14: Main Color Board Digital Theory of Operation
14-4
14.2.2 Microcontroller Signals
The power supply circuit and microcontroller have 2 signals which connect
directly with each other, EARLY
WARNING and PSOFF. The battery circuits
generate an EARLY WARNING signal to the microcontroller to warn it that the
power is going down within 100 ms. This EARLY WARNING signal is
generated if the power
On/Standby
switch is pressed or the battery voltage gets
too low. The signal is connected directly to INTERRUPTS
5
and 7. The
software will save any information it must save and finish its housekeeping
before sending the PSOFF signal back to the battery circuits.
14.2.3 MEMBRANE SWITCHES/POWER SUPPLY
The power supply circuit connects directly with the
On/Standby
switch and the 2
LED’s on the membrane switch. The
On/Standby
switch goes directly from the
membrane switch to the power supply board via the 50 pin cable. This is to
allow powering up when off. Another switch also goes to the battery circuit, the
A
larm Silence
switch. Unlike the
On/Standby
switch, this switch also goes to
the microcontroller.
14.2.4 POWER SUPPLY GENERATED LED SIGNALS
The power supply circuits generate two LED driving signals, one that indicates
that the AC mains is connected, and one which indicates that the DC power is
connected. When the
AC MAINS
LED is being driven on, a high voltage level
goes to the 386EX port 1 bit 6 as the AC mains input status bit. When the LED
is off the signal is a logic low. The software will interpret the signal levels so as
to tell whether the AC mains is connected or not. The same is true with the DC
power input connector. The signal driving the DC led goes to port 1, bit 7. This
indicates the DC power status.
14.2.5 BATTERY SIGNALS TO THE A/D CONVERTER
The battery voltage signal is sent to the main board where it is buffered by an
amplifier circuit which converts it to a signal in the 0-5 volt range of the A/D
converter. The signal is sent directly to the main board and is
divided by 2 by a resistor divider circuit on the positive input to the amplifier.
The amplifier has a gain of 2, which brings the signal back to its original signal
level and then we resistor divide it to the 0-5 volt range for the A/D converter.
14.2.6 SYNC/ALARM 50KHZ SIGNAL
The power supply needs a 100 kHz signal to synchronize its own internal
operation and to keep the alarm from sounding. The 100 kHz signal is “anded”
with the watch dog timer (WDT) and if the WDT should time out the power
supply circuit will sound the alarm and shut down the main board.
Summary of Contents for NELLCOR NPB-4000
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