GE MAC 5500, Service Manual

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2-32 MAC

5500 resting ECG analysis system Revision E
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2020299-020
Equipment Overview: Theory of Operation
Moe
Moe is responsible for controlling and monitoring the battery, power supplies, on/
off key, system reset and related functions. Moe runs continuously from +3V-C,
even in the absence of AC power. This continuous operation is necessary for Moe to
accurately monitor the battery state of charge and detect power key presses.
System Startup
When the system is off and the user presses the power key, Moe begins the startup
sequence. If the battery contains sufficient charge, or if AC power is applied, the
main CPU board power supplies (+3V-M and +5V-M) are enabled and after a
suitable stabilization period SYSRESET* is released. Moe then keeps tabs on the
system via a software watchdog that must be serviced by specific BBus activity
from the ATMEL CPU. 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, which it controls, are off when it
powers up. If Moe should malfunction while the system is already powered it is
likely that the HC05 will incorrectly identify itself as Larry. Larry’s default
power-up state results in its port pins assuming a state that di3V-M.
Since Larry does not service the watchdog chip (WDOG), another reset will
follow within 2 seconds. As +3V-M is now down, Moe will be selected at the
next restart.
When SYSRESET* is released, ATMEL CPU configures the FPGA and load
secondary boot program from information stored in NAND Flash. Moe expects the
ATMEL CPU to request status via the BBus interface after startup. If that request
doesn't arrive in time, Moe places the system back in reset and removes power. The
time is set as two minutes six seconds for this version. This time-out considers the
time for software update. There is a provision to disable the Moe watch dog monitor
using jumper W1. This is to facilitate the debug tool connectivity.
In the event of main CPU failure that causes loss of function yet maintains Moe’s
watchdog function, a manual forced power-down function is provided. A continuous
press of the power key for a period greater than 5 seconds will force the system to
shutdown.
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 5500. Located in the bottom of the chassis, the power supply is
disconnected from the CPU board when the lid is open. The battery connection is
maintained through the hinge so the CPU board is capable of operating for a limited
time with the door open.
An LT1511 switchmode charge controller (Battery Charger) provides battery charge
current. This device monitors both battery and power supply current draw and
maintains both at safe levels. As system current draw increases, the Battery Charger
automatically decreases battery charging current to maintain total power supply
current below the design level (nominally 1A). Nominal charge current is also 1A,
which is achievable only when the system is off.