Schiller AT-1 - Control and Power Supply board MK II - 1

Chapter 2
Funcrionai Overview
SCHILLER AT-1 3-Channel ECG Unit
SERVICE AGWDBOOK Issue 3 September 1999
Control and Power Supply board LMK I1 - L
Power Supply
The mains suuply is full wave rectified to produce an unregulated dc supply of approximately
35V(+U). This voltage is used by a switched voltage generator to produce +UD (13.jV). +UD
charges the battery wnen mains is connected. When mains is not connected, +UD is the battery
voltage.
An
ON/OFF control logic switches +UD to three voltage regulators. The unit is switched on
directly from the keyboard and then held on from the CPU (signal !J,PO~. Detection of
overvoltage on either the 5.2V or 24V supplies directly switches the unit off. Similarly when an
undervoltage is detected on +us (indicating over current) the unit is directly switched off.
The mains LED is lit directly when mains is connected. The same circuit also monitors the switched
dc supply
(+US) and activates signal +BAIT when the unit is switched on and mains is not
connected (i.e.
the unit is running on battery power).
A Battery low signal (BLOW) is generated when battery voltage (+US) falls to 11.3V. A circuit
compensates
for voltage drop when the printer stepper motor is active and the Blow signal is active
only
at 10.3V.
Note:
The bartery voltage is also monitored directly by the CPU which switches the unit
off (p0FF) when the voltage falls below approximateiy 9.4V.
CPU and Processing Circuits
Overall control and coordination of the AT-1 is by 68332 CPU which performs all timing and
control functions.
Memory
Program Memory
An EPROM contains the unit software. The EPROM has 128 kByte of memory.
Static RAM Memory
The RAM memory stores the ECG data and comprises two 128 kbyte RAM chips. All data are lost
when the unit
is switched off.
Serial EEPROM
The serial EEPROM (U12) stores the unit base settings.
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