91369 Service Manual
3-11
Theory
MII
The MPC8270 has all the MII pins except bi-directional data line (MDIO) and MDC (clock), which are provided
between the PHY chip and MPC8270 GPIO.
• MDIO
→
PC4
• MDC
→
PC3
Fast Ethernet PHY
An Intel LXT972A is used for Ethernet PHY. This is an IEEE-compliant Fast Ethernet PHY transceiver
supporting both 10BaseT and 100BaseT applications.
SDLC Interface
The SDLC bus is the communications interface to Spacelabs Healthcare modules, which supply patient data to
the monitors. The SDLC interface runs at 1.892352 MHz. This is divided down to generate a 448 Hz sampling
rate. The SDLC communication task retrieves the data from the bus, assembles it into a packet format, and
provides it to the monitor application. The SDLC clock signals are output by the SDLC interface and are used
to drive the external SDLC bus and modules. The SDLC data signals are bi-directional and can be used to both
transmit and receive data from the intelligent modules.
RS-232 (UART)
The RS-232 universal asynchronous receiver-transmitter (UART) uses some UART signals for communication
with external devices. Linear Technology LTC1331 RS-232 transceivers are used to provide 3 V interface with
the MPC8270. Communication with external RS-232 devices is through the 9-pin DSUB connector and
transmission speed is limited to 9600 Kbps.
Embedded Alarm Light
A “flexible circuit” and PCBA contain circuitry for the embedded alarm light. Five ultra-bright LEDs are used for
each color (red, yellow, and cyan) to generate the back light for the lens.
Because alarms are available on the monitor as well as externally, an internal signal is provided (from pin
PB26 on the MPC8270), allowing the software to enable/disable the embedded alarm light on the monitor.
At initial power ON, the LEDs cycle through at a rate of 4.2 Hz for a duration of two seconds, which is more
rapid than the fastest flash rate used for any alarm condition (2.8 Hz). This function allows the user to confirm
that all the LEDs are functional.
Optical relays are used for both the embedded alarm light and the external alarm relay output.
External Alarm Control
During boot diagnostics, all three alarm relays are tested for two seconds. During normal operation, the high-
priority alarm relay is activated during high-priority alarms (for example, heart rate), and the medium-priority
alarm relay is activated during medium-priority alarms (for example, leads off).
