Schiller CARDIOVIT AT-1, Руководство по обслуживанию

Страница: 42 / 84

42
Main Board MK 11-10
Power Supply
The mains supply is full wave rectified to produce an unregulated dc supply of
approximately 35 V (+U). This voltage is used by a switched voltage generator to produce
+UD (13.5V). +UD charges the battery when mains is connected. When mains is not
connected, +UD is the battery voltage.
An ON/OFF control logic swUD to three voltage regulators. The unit is switched
on directly from the keyboard and then held on from the CPU. Detection of overvoltage
on either the 5.2 V or 24 V supplies directly switches the unit off. Similarly when an
undervoltage is detected on +US (indicating overcurrent) 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 BATT 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 set to logic 0 when battery voltage (+US) falls to 11.3 V. A
circuit compensates for voltage drop when the printer stepper motor is active and the
BLOW signal is active only at 10.3 V.
Note : The battery voltage is also monitored directly by the CPU which switches the
unit off when the voltage falls below approximately 9.4 V.
CPU and processing circuits
Overall control and coordination of the AT-1 / AT-1smartprint is performed by a Motorola
68332 Microcontroller, which performs all timing and control functions.
Memory
• An EPROM with 128 kByte memory contains the unit software.
• A static RAM memory stores the ECG data and comprises two 256 kByte RAM
chips.
• A serial EEPROM (U48) stores the unit base settings.
Thermal Printhead Controller
The thermal printhead is controlled by a printhead controller and a CPU timer circuit.
The printhead controller serialises the data for the printhead and the timer circuit controls
how long current is applied to the head, and thus the intensity of the printout.
Printer Timing
Strobe generation is controlled by the CPU when one complete pixel line of data is
ready to be written. Pulse length of STRB1 and STRB2 (each of which controls half of the
pixel array) depends on the TPH temperature and therefore on the pulse width of the
TPHT signal.
Note: TPH temperature reading is described on page 34.