GE MAC 5500, Service Manual

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2-12 MAC

5500 resting ECG analysis system Revision E

2020299-020
Equipment Overview: Theory of Operation
VAna+, VAna-
The analog output circuitry is powered by a low current switched 12V rail, provided
by the Main Regulator. VAna+ provides the positive supply for the output op-amps.
A charge pump voltage inverter is provided to produce an approximate -11V rail for
the op-amps. Although only the ECG output is bipolar, all output amplifiers are
driven from VAna-. A short circuit on either of the unipolar DC outputs could load
VAna- sufficiently to affect the negative peak swing of the ECG output. The ECG
and DC outputs are not required to operate correctly in the presence of abnormal
loads.
Clocks
Super I/O and FPGA
Both of these devices uses the 24 Mhz clock oscillator Y5 to drive their internal
requirements for various clock frequencies. The main function of the Super I/O IC is
for serial port communication and real time clock; all the needed timing comes from
this oscillator. The FPGA provides many functions including the acquisition
interface, the printer interface, and the Stooges interface (Bbus) to name a few. The
FPGA uses a built-in frequency doubler to raise this 24 Mhz clock to 48 Mhz for
internal use. All functions inside the FPGA use the clocks derived from 48MHz. The
main derived clocks are:
 1 MHz for acquisition interface

4 MHz for printer data shift clock interface.
 4 MHz for EEPROM data shift clock

24MHz for VGA LCD panel clock.
The VGA LCD controller, that include the SDRAM frame buffer controller use
59.904 MHz external memory clock from ATMEL CPU in addition to the 48MHz
FPGA clock
CPU ATMEL AT91RM9200
The ATMEL AT91RM9200 has two oscillators. Slow Clock oscillator and Main
Oscillator. The Slow Clock Oscillator uses 32,768 KHz crystal for clock generation.
The CPU runs in Slow Clock mode (@48MHz) after system reset. Slow clock is
also used by the built in RTC. The CPU does not use the ATMEL RTC for the
system timing requirements. The Main oscillator uses 18.432 MHz crystal.
Processor clock (179.712 MHz), Master clock (59.904) for external Bus Interface
and Peripheral Clocks are derived from main oscillator by the Master Clock
Controller.