Structure and Assembly/Disassembly of the Machine
In the portable ultrasound diagnostic system, the watchdog is only used for power-on
reset, so the SDA pin of the watchdog can be directly connected to a clock through
CPLD. Therefore the watchdog will be disabled after the system is reset.
2.1.2.3System clock circuit
The chip 5307 has the doubling circuit internally, so the core frequency of CPU is twice
the external bus frequency. The external frequency of 45MHz is adopted, and the
operating frequency of CPU is 90MHz. If a peripheral device operates synchronously with
the CPU, the external frequency of 45MHz must be applied.
The distribution of the 45MHz external frequency clock of CPU is shown below:
Figure 3-9 CPU system clock distribution
2.1.2.4Voltage detection circuit
The voltage detection circuit is designed for the detection of eight voltages of
＋
5V,
－
5V,
＋
1.5V,
＋
2.5V,
＋
3V,
＋
13.5V, +12V and PHV (programmable high voltage).
Except the
＋
1.5V voltage, other voltages are converted into the
＋
2.5V voltage by
means of voltage divider or inverter.
PCF8591 is used as the voltage detection chip, which has 4-channel analog inputs. So
two pieces of PCF8591 are required. LM4120 is used as the reference voltage source,
supplying the
＋
3.3V voltage.
The
＋
3.3V reference voltage can tolerate certain forward bias. If the 2.5V voltage is
set as the input voltage under detection, the overload range is 30% (
（
3.3-
DP-3300/DP-3200 Service Manual（V1.1） 3-13
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