GE Solar 8000M/i Service Manual page 37

2026265-075C
Equipment overview: Theory of operation
The Serial Management Interface (SMI) to the Broadcom Ethernet
Switch is provided by reprogramming SCC3 in the MPC860 to be an
HDLC controller and setting the appropriate MPC860 port pins to get
the proper muxing action within the FPGA. The use of the SMI is to
determine which M-Ports have a functioning 10BaseT Ethernet
connection on them without having to switch the relay back to ID mode
and interrogate for a One-Wire interface.
NOTE
The clock source for the SMI is selected by the MPC860 to be either
sourced by itself or by the Broadcom Ethernet Switch under software
control.
M-Port power sourcing – Each M-Port is capable of providing
+5V +/- 5% @ 100mA into an external load.
Isolation – Per the M-Port Specification, Basic Insulation for 250Vac is
provided between each M-Port and any other isolated facility and from
earth ground.
ESD protection scheme – The M-Port connectors are ESD protected
by using the planar capacitance method since they are isolated from an
earth connection. The typical diode/transzorb pair is employed to clamp
the connector pin to its isolated return plane. The impedance of the
connector contact, the ferrite bead and the copper traces form an
impedance divider with the 'planar' capacitor formed by the dielectric
material in the PCB layer between the copper of the isolated return
plane and the copper of the common (earthed) plane. The expectation is
that the physical impedance divider formed by the bead/trace/connector
inductance and the planar capacitor will accomplish the following two
results:
Limit the rate of rise of the voltage across the isolation barrier, i.e.,
across the planar capacitor, and
Limit the peak amplitude to which the voltage across the barrier
rises to.
RS-232 serial ports
Both RS-232 serial ports are associated to a video set as described earlier
to accommodate a touchscreen. However, the serial ports are not limited
to being a touchscreen interface only. The RS-232 1 port also interfaces
to the iPanel computer and either of these serial ports are capable of
providing a polled data service facility or can be used as a service port.
Processor SMC channels – The RS-232 1 uses the SMC1 and the RS-
232 2 will use SMC2 in the MPC860.
Isolation – The serial ports are not isolated with respect to earth
ground.
ESD protection scheme – The typical diode/transzorb pair is employed
to clamp the RS-232 serial port connector pins to the common return
plane. Since the serial ports are not electrically isolated, the need for
maintaining isolation in the ESD protection scheme is not present.
Solar 8000M/i patient monitor 2-21