 of pager memory and are called up by transmitting a numeric code. For cell since suitable button cells are not freely available outside N. alphanumeric pagers which require greater memory storage for America and major European countries. As a battery life of 800 to received messages, static RAMs working from 5 volts and capable 900 hours or about 2 to 3 months, depending on paging receiver and of storing 6000 characters are used, the disadvantage with these system usage, is required then the AA cell is widely used. With devices is that they need separate battery backup. For numeric improvements in circuit techniques and world wide availability, the pagers which are only required to store short numeric messages the Private wide area paging 45/15 RAM of the microprocessor can be used without battery backup. order to improve transmission distance within a system. A sequence The advantage of 3 volt read/write EEPROM is that off air pro- of time slots can be allocated to one user where the system has a gramming is possible where the pager receives reprogramming high call rate. The ZZF issue a range of address codes to the information transmitted to it from the base station. The low voltage manufacturer upon equipment approval. means it can rewrite its own memory. 45.10 Pan-European systems Private wide area paging 45.10.1 Euromessage 45.9.1 Overlay paging This system (Table 45.7) opened late 1989 and is now operational Overlay paging is a system where paging addresses are sent over a in major towns and industrial regions in France and West Germany, PMR two way vehicular radio system to directly alert the driver, in the UK in London and Home Counties, and some parts of Italy. who has temporarily left his vehicle, to the fact that a message Full messaging is possible in each individual country and the com- awaits his attention. Such additions to PMR schemes are permitted, mon specification is shown below. Additional features are added though in the UK they are subject to the following conditions: according to the Natio