GE MAC 5000 Service Manual page 54

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Equipment Overview: Theory of Operation
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 disables +3V-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 5000. 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.
Moe enables / disables the charger via CR102. When Moe pulls the
CHRGTRL line low, CR102 sinks current from the Battery Charger's VC
pin shutting down the error amplifier and disabling switching. R120
ensures that the charger remains off when Moe is starting up.
MAC™ 5000 resting ECG analysis system
2024917-010
Revision B