A reference address is assigned to discrete output modules using the Logicmaster 90-30/20/Micro configuration software or the Hand-Held Programmer. Until a reference address is assigned, no data is sent to the module. A particular %Q reference may be either retentive or non-retentive. %M The %M prefix represents internal references. The dual use coil checking function of the HHP software checks for multiple uses of %M references with relay coils or outputs on functions. Beginning with Release 3 of Series 90-30 and Release 2 of Series 90-20 firmware, you can select the level of coil checking desired (SINGLE, WARN MULTIPLE, or MULTIPLE). Refer to Chapter 3 for more information about this feature. A particular %M reference may be either retentive or non-retentive. %T The %T prefix represents temporary references. These references are never checked for multiple coil use and can, therefore, be used many times in the same program even when coil use checking is enabled. Because this memory is intended for temporary use, it is never retained through power loss or RUN-to-STOP-to-RUN transitions and cannot be used with retentive coils. %S The %S prefix represents system status references. These references are used to access special PLC data, such as timers, scan information, and fault information. System references include %S, %SA, %SB, and %SC references. %S, %SA, %SB, and %SC can be used on any contacts. %SA, %SB, and %SC can be used on retentive coils -(M)-. %S can be used as a word or bit-string input reference to functions or function blocks. %SA, %SB, and %SC can be used as a word or bit-string input or output reference to functions and function blocks . %G The %G prefix represents global data references. These references are used to access data shared among several PLCs. %G references can be used on contacts and retentive coils because %G memory is always retentive. %G cannot be used on non-retentive coils. Transitions and Overrides The %I, %Q, %M, and %G user references have associated transition and override bits. %T, %S, %SA, %SB, and %SC references have transition bits, but not override bits. The CPU uses transition bits for counters and transitional coils. Note that counters do not use the same kind of transition bits as coils.
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