GE MAC 5000, Field Service Manual

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Revision B 5-16
CPU Theory of Operation: Theory of Operation
MAC 5000 resting ECG analysis system
2000657-002
be serviced by specific BBus activity from the StrongARM. Moe himself
is monitored by a self contained MAX823 watchdog timer / brownout
detector. Moe must constantly toggle the MAX823 watchdog input pin
or suffer the consequences.
Note: Moe presumes that the main power rails are off when he powers
up. If +3V-M is up when Moe restarts the self ID code will incorrectly
assume that Moe is actually Larry. As +3V-M is controlled by Moe, this
should never happen. Even if Moe halts while operating, the minimum
MAX823 reset period of 100ms virtually guarantees that +3V-M will be
down before Moe comes out of reset (HC05 port pins tri-state in reset
and the main power enable input to the MAX782 switching regulator is
pulled down by a resistor).
When nSysReset is released, Curly configures the FPGA and starts the
StrongARM from information stored in the SmartMedia card. Moe
expects the StrongARM to request status via the BBus interface within a
few seconds of startup. If that request doesn’t arrive in time, Moe places
the system back in reset and removes power.
AC Power/Battery/Charger
Battery and system power management is entirely Moe’s responsibility.
An off-the-shelf 28V 1A universal input power supply provides
operating/charging power for the MAC 5000. Located in the bottom of
the chassis, the power supply is disconnected from theCPU when the lid
is open. The battery connection is maintained through the hinge, so the
CPU is capable of operating for a limited time with the door open.
A self-aligning connector routes power and motor signals from the
power supply compartment to the CPU. When the lid is closed the
DoorOpen signal is shorted to ground. When the lid is open a pullup
resistor ensures a high level on DoorOpen. Moe monitors this line to
detect lid open conditions which are reported to the system software to
avoid misinterpretation of motor fault indications. When the door is
open, the motor connections are lost and Larry receives no tachometer
feedback from the motor. Without knowing the cause of the lost tach
info, Larry can only respond with a paper jam condition. Moe’s
knowledge of the lid state is used to suppress this error message as well
as prevent further print operations.
AC Power Monitor
Moe senses the presence of AC power. The battery charger will not be
enabled unless AC power is detected.
Ambient Thermistor
Extreme hot/cold ambient conditions are not favorable for battery
charging. Rapid changes in ambient temperature can cause premature
or delayed charge termination by altering the packs temperature. Moe
monitors ambient temperature to ensure that charging occurs only
within the "safe" temperature range as well as to minimize the effects of
changing ambient temperature on charge termination (particularly to