uniphy Phyaction 740 Series, Service Information

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Service Information Phyaction 740 & 790-series Page 16
2.2.1 Microcontroller core
As central processing unit a microcontroller is being used in favour of a microprocessor. The reason
being that a microcontroller, by its construction and available commands, is particularly suited for bit-level
operations. From the software point of view there is no difference but it is much easier to manipulate a
single I/O-pin. The microcontroller used in the Phyaction 790-series is the 80C552. It incorporates in
addition to the actual 8051 controller the following circuits:
- 256 Byte RAM
- 3 programmable timers
- 1 A/D-Convertor with eight multiplexed inputs and 10-bits resolution
- 5 I/O ports, each 8 bits wide
- 2 Pulse width modulators with 8-bits resolution
- 1 I²C-bus interface for internal data transmission
- 1 full-duplex UART (Universal Asynchronous Receiver and Transmitter)
- 1 Watchdog timer
Apart from this microcontroller the core contains the following devices:
- an 8-kbyte RAM with integrated lithium battery (NOVRAM)
- a 1-Mbit EPROM
- a programmable I/O-expander
- an analog multiplexer to increase the amount of ADC inputs
- some PAL's and HCMOS chips as decoders and buffers
2.2.2 User interface
A LCD (Liquid Crystal Display) with a console forms the major link in the communication between the
operator and the microcontroller. The display is connected directly to the microcontroller via the data-bus
and the keys of the console via the I²C-bus. The menus and program screens are shown on the display
and the operator selects the requested therapy with the buttons and also changes or enters parameter
settings with them.
2.2.3 Serial interface
A serial interface identical to that in the Phyaction 780-series is provided to be used with future
extensions. The way of operating is similar to that of the teletype current loop although the level of the
current has been reduced. The interface is fully isolated from the rest of the circuits in the appliance by
means of optocouplers with an isolation voltage of 2.5 kV.
2.2.4 Parallel interface
This unit, which is only present in the VIP versions, makes up the link between the LCD and the I/O-card
in the PC. Again using optocouplers with an isolation voltage of 2.5 kV to achieve full galvanic isolation,
the necessary control-signals are tapped and the data is synchronously stored in a RAM. This RAM in its
turn is being asynchronously read by the software running on the PC which subsequently reconstructs
the image shown on the LCD.
2.2.5 Power supply
The power supply is of a conventional linear design with a mains transformer for medical devices
followed by secondary fuses, bridge rectifiers and smoothing capacitors. From the unstabilised voltages
created in this way, the one 29V is used to supply the power stages for the current generation
and the ultrasound generation. The other supply voltages, +24V, +15V, -15V and +5V (Vcc), are
stabilised by linear regulators with the latter three in addition being protected from overvoltages by
crowbars. A reset signal is issued to the microcontroller when the +5V (Vcc) is beneath the threshold