General Service Guide
9
Document No. 896 623
2
SYSTEM DESCRIPTION
2.1
Introduction
Datex-OhmedaAS/3 and CS/3 monitors builds up to freely configurable modular system. The
architecture is designed to enable different module combinations so that the user is able to get the
desirable parameter and feature set. The modular approach makes it possible to add new features
when they are needed.
2.2
Bus structure
The operation of Datex-OhmedaAS/3 and CS/3 products is based on two communication
channels, the
CPU bus
and the
module bus
. All boards connected to the CPU bus as well as the
parameter modules attached to the module bus receive their power from the same power supply,
which is an integral part of the frame.
Parameter
Module
Display
Controller
MODULE BUS
CPU BUS
CPU
Power
Supply
Parameter
Module
UPI /
UPINET
Figure 2
General Structure of AS/3 and CS/3 System
The CPU bus is a parallel communication channel used only for internal data transfer between the
boards connected to one frame. It is based on the ISA bus used in the IBM PC computers. Data is
transferred on this 16 bits wide bus using the CPU clock frequency.
The module bus is used to connect the parameter modules to the frame. It based on the widely
used industry standard RS-485, which uses differential serial method to transfer the data. This
type of bus is quite robust and it allows the modules to be attached or detached when the power is
on.
The RS-485 type serial communication supports so called multidrop or party line connections. This
means that all modules connected to module bus are using the same two physical wires for
communication purposes. The advantage is, that all the module bus connectors are identical and
the modules can be connected to any order and position.
Module bus is using 500 kbps data transfer rate and it can be used for longer distances than the
CPU bus, e.g. for external-frame connections.
