Datascope Passport 2, Руководство по обслуживанию

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Passport 2®/Passport 2 LT™ Service Manual 0070-10-0441 2 - 11
Theory of Operation CPU Control Module
2.1.30 Control Functions
There is a DC/DC converter module, PS1 which provides isolated DC power to the front end
circuitry. The module can be turned on by a logic 1 on the Communications Processor port
pin PGP7.The Communications Processor reset input is controlled by a signal from the
MPC860T, port pin PA(6). The signal required for reset is a logic 1. The signal is inverted by
FET Q1 before being connected to the Communications Processor RESET* pin.
2.1.31 Module Bus
Communications with all measurement modules in the ECM is through a RS-485 module bus.
The Communications processor is the host and all modules are slave devices. The
Communications Processor UART connects to the module bus through RS-485 buffer/driver
U20. The direction of the data flow through the RS-485 buffer driver is controlled by two
different signals from port pins on the Communications Processor. Receive is controlled by an
logic 0 on port pin PGP6 and logic 0 on PGP0 Transmit is controlled by a logic 1 on PGP0
and a logic 1 on PGP6.There is a module bus connection from the isolated front end through
RS-485 buffer driver, U28. The isolation is provided by opto couplers. The front end transmit
data is provided by opto coupler U230 and receive data by opto coupler U231 along with
Q2 and part of U100. The direction of data flow is controlled by opto coupler U232 along
with part of U100.