IEC 62056-21 “Flag”

 Introduction 

IEC 62056-21 is the third edition of the well-known IEC 1107 standard, also known as the “Flag protocol”. Although it was intended for local data exchange using hand held units (HHU), it is also widely used for remote data exchange with PSTN and GSM modems.It specifies three local physical interfaces: optical, current loop and V.24 / V.28, as well as a data transmission protocol. The protocol permits reading and programming of devices, basically by reading and sending information represented by ASCII characters to / from given memory locations.

Like 1107 ,the following communication modes are available: 

• Mode A supports bi-directional data exchange at 300 baud without baud rate switching. This protocol mode permits data readout and programming with optional password protection; 

• Mode B supports bi-directional data exchange with baud rate switching. This protocol mode permits data readout and programming with optional password protection;

• Mode C supports bi-directional data exchange with baud rate switching and permits data readout, programming with enhanced security and manufacturer-specific modes; 

• Mode D supports unidirectional data exchange at a fixed baud rate of 2400 baud and permits data readout only; 

• Mode E supports advanced protocols, like DLMS/COSEM. 

The mode can be negotiated by the HHU and the meter. A meter can support more than one mode: today, support of Mode C and Mode E with DLMS/COSEM is common practice. 

Status of standardization  

The current standard has been established by IEC 62056-21 WG 14:. IEC 62056-21 Ed. 1.0:2002,  Electricity metering – Data exchange for meter reading, tariff and load control – Part 21: Direct local data exchange (third edition of IEC 61107) The standard is open and widely used. However, the memory mapping is not standardized, therefore data exchange requires manufacturer specific information. Meters of different types or from different manufacturers are not readily inter-operable: each meter type needs a specific driver. Annex C of the standard specifies formatted codes, but these are not widely used. 

Support organization 

The mandatory three-letter manufacturer identifiers are allocated by the FLAG Association, in co-operation with the DLMS User Association. The same identifiers are also used for DLMS/COSEM. Some three hundred manufacturers have obtained their manufacturer ID. 

See at: http://www.dlms.com/organization/flagmanufacturesids/index.html

Data model 

Not available in modes A to D, data are located and manufacturer specific memory addresses.  In Mode E, the COSEM data model and protocol stacks are used. 

Communication media supported 

The current loop is a local bus supporting up to eight meters. PSTN and GSM are supported with appropriate modems. 

Summary 

This protocol was the first standard protocol for meter data exchange and is globally used. 

Today, its main use is for local data exchange.