An introduction to MAP

An introduction to MAP
As early as the late 1970s, General Motors in the USA were estimating that over 50% of automation costs
within GM were going into communications functions, and the continual lack of well-defined standards
was seen simply as adding to this cost. This led in November 1980 to the establishment of the MAP
(manufacturing automation protocol) task force. 1988 saw the publication of the MAP 3.0 specification
and to this date several PLC manufacturers have released MAP 3.0 compatible interfaces.
Where does MAP however fit into the scheme of things as a PLC user? The concept of MAP was really
designed for inter-computer communication, ie large volume data and file transfer. At the PLC, cell
control level, control and data transfer is required to be 'realtime'. This led initially to the concept of Mini
MAP. Mini MAP is completely non-MAP compatible and is designed to inter-connect low-cost devices
via a time-critical network which could ultimately be linked to a carrier-band MAP backbone.
Field bus
This Mini-MAP concept led to the drive to specify a non-MAP compatible, low cost, real-time bus which
would inter-connect devices at the lowest level. Such buses were termed 'field buses', but even here
standardisation seems far off.
Intel already had in existence its Intel Bit Bus which had many of the characteristics required. Based on
RS485 at the physical layer, it could communicate with both field devices and PLCs at up to 1200 m
using twisted pair cable and standard connectors. A few European PLC manufacturers immediately
adopted this standard.
This Bit Bus, however, was also seen to have a major shortfall, in that it was based on a master-slave
topology. At this time, the major field-bus standard contenders are Profibus, Modbus Plus and FIP Bus.
We look at the first of these:
Profibus
Most of the PLC and field device manufacturers in Europe got together in the late 1980s to set up the
Profibus (process field bus) working group. The specifications generated out of this group for a standard
field bus communication were: