S4 Circuit Analysis; S4.1 Functional Overview - NELLCOR PURITAN BENNETT Symphony N-3000 Service Manual

S4 CIRCUIT ANALYSIS
S4.1 Functional Overview
The external stackbus is used for communications between the N-3000 and
the N-3100. Information is exchanged over two pins on the N-3000 docking
connector and two sockets on the N-3100 upper docking connector. As with
the internal stackbus, the Arcnet local area network standard is used as the
protocol. RS-485 drivers and receivers are used for signaling. A proximity
sensor in the bottom of the N-3000 or N-3100 detects when the monitor is
docked, enabling the stackbus signals.
Access to the stackbus is accomplished through token passing. A token
designates which station (module or instrument) has control of the stackbus.
The token is passed in a circular manner from station to station. The station
holding the token has the exclusive right to transmit onto the stackbus, but
the right to transmit may be temporarily donated to another station to
acknowledge a transmission by the token holder. The token holder must
relinquish control of the stackbus by passing the token to the next station on
the loop within a specified period of time. During normal operation, the right
to access the stackbus passes from station to station in a continuous,
consistent manner.
All instruments participate in the loop when stacked and powered-on.
Maintenance of the token passing, loop initialization, lost token recovery, and
the addition of new stations is implemented in the N-3000's UIF and SpO
modules and in the N-3100 by the specialized devices and system software.
This section provides a descriptive overview of the N-3000 modular design, as
well as a circuit description.
The monitor functional block diagram is shown in Figure S4-1. Central to the
PCB modules is the UIF module. This module receives power from an
external AC source or battery via the docking connector. It supplies power to
the other modules connected to it, while also communicating with them via
the stackbus. It controls user interface and network gateway functions.
Connected to the UIF module is the SpO
PCBs: the SpO Controller and the SpO
2
contains the micro controller, memory system, internal stackbus interface,
and other control logic. The SpO
conditioning and control hardware necessary to measure SpO
boards are electrically connected by a single interface connector.
The Communications module allows messages to be sent to a host computer
using asynchronous serial communications. All communications signals on
the Communications module originate from the UIF module.
The Display module contains annunciators and push buttons, allowing the
user to access information and to select various available parameters. The
Display PCB contains SpO
circuits. Front-panel switches also allow the user to turn the unit on and off,
to set alarm limits and to print data. The Display PCB is connected to the
UIF module via a 14-pin connector.
module, which consists of two
2
PCB. The SpO
2
PCB contains all the analog signal
2
and heart rate LEDs and their associated driver
2
Technical Supplement
2
Controller board
2
. The two
2
S-3