Biomedical Engineering Reference
In-Depth Information
180 ms beyond activation of the RV. This would be considered an intrusion into the
“vulnerable period” of the heart.
A and V event timers . The A and V event timers are incremented each time through
the TIMER1 interrupt service routine. These timers are used to calculate the time
since the last A and V events.
Right-ventricle event to left-ventricle sense delay timer . The right-ventricle event to
left-ventricle sense output time delay, if not equal to zero, is decremented each time
through the TIMER1 interrupt service routine. If after decrementing the timer, the
timer is equal to zero, the left-ventricular sense waveform output is started. The delay
is read from the front-panel hex thumbwheel switch.
LED timers . Each LED on the front panel is on for a
fixed length of time. The on time
for each LED is loaded into a timer when the LED is switched to the on state by one
of the subroutines. Each of the LED timers, if not equal to zero, is decremented; after
decrementing, if the timer is found to be equal to zero, the LED is switched off.
fi
.
Delay timer . A general-purpose delay timer, if not equal to zero, is decremented each
time through the TIMER 1 interrupt service routine, and if after decrementing is
equal to zero, the DELAY_FLAG is cleared.
Test ECG out . Check to see if the ECG waveform output
ff
fl
flag is enabled (ECG_
flag is enabled, write the next word in the ECG waveform table to
the ECG D/A converter.
Test Z out . Check to see if the Z waveform output
FLAG
1). If the
fl
fl
flag is enabled (Z_FLAG
1). If
the
flag is enabled, output the next word from the impedance waveform table to the
impedance D/A converter.
fl
The second section is the TIMER0 interrupt service routine, which is executed once
every 200
µ
s:
Test port B inputs . Check if any of the inputs on the upper 4 bits of port B went from
a low to a high state. If the enable
fl
flags for each of these inputs is set to a 1, the event
fl
flag for each input is then set to a 1. The event
fl
flags are used to signal that one or more
external events have been detected.
Test the PVC switch input . Check to see if the PVC switch was pressed and that a
LV_PVC_ENABLE event is not already pending. If not, signal an LV PVC event by
setting the LV_PVC_ENABLE
ag.
Test A out . Check to see if the right-atrial CENELEC waveform output
fl
fl
flag is enabled
flag is enabled, write the next word from the CENELEC wave-
form table (CEN_TABLE) to the A sense D/A converter.
Test V out . Check to see if the right-ventricular CENELEC waveform output
(A_FLAG
1). If the
fl
fl
flag is
flag is enabled, write the next word from the CEN-
ELEC waveform table (CEN_TABLE) to the V sense D/A converter.
Test LVS out . Check to see if the left-ventricular CENELEC waveform output
enabled (V_FLAG
1). If the
fl
fl
flag is
enabled (LVS_FLAG
flag is enabled, write the next word from the CEN-
ELEC waveform table (CEN_TABLE) to the LV sense D/A converter.
1). If the
fl
When Radio Shack Parts Are Not the Answer
Responsive simulators such as the one described earlier can be designed to emulate the
deterministic behavior of a biological system. There are occasions, however, when the rel-
evant physical properties of the biological system are too complex for simulation with
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