ZOLL PD 2000 - Page 79

SERVICE MANUAL
ECG Data Interface
Four optoisolators provide the interface to the isolated side:
Output ECG_DATA_IN Serial eight bit ECG data.
Input EDATA_OUT_CLK Data clock for both
directions of data.
Input ECG_LATCH Used to set the eight bits of
the isolated side latch:
Input ECG DATA OUT | ECG control word
two bits: four lead combinations |, IL
III, paddles
three bits: eight ECG amplifier gains
two bits: three bandwidths
one bit: LEAD DRV, strobes lead
select relays.
System Side
Power Supply for Patient Isolated Circuits
The supply chopper signal is provided by the CPU gate array at 50 kHz.
The signal is buffered (Q117, Q119) to drive the power chopper.
5B. CRT DEFLECTION CIRCUIT
Deflection
Two similar deflection circuits receive X and Y deflection analog voltages
from the EPU and convert them to deflection currents to drive the CRT
beam. These circuits are based on operational amplifiers which convert
= input voltage to current in the range of 0.6 amps and include filtering to
remove DAC steps and provide compensation.
Both circuits operate in high and low power modes to conserve battery
capacity. With slow beam movement, power is derived from +/- 4.2 volt
supplies. When the beam is required to move rapidly, power is switched
momentarily to +/- 11.6 volts to achieve more rapid change in deflection
coil current.
CRT Intensity Control
The intensity control circuits have three operational sections. They are a
high slew signal which is a rectified signal proportional to beam rate of
change, INT_2, a high slew inhibit switch, and an adjustable current
source (Q100 and R123) to control cathode voltage.
TV-20