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6-8 489 Generator Management Relay GE Multilin
6.3 MODBUS MEMORY MAP 6 COMMUNICATIONS
6
6.3MODBUS MEMORY MAP 6.3.1 MEMORY MAP INFORMATION
The data stored in the 489 is grouped as Setpoints and Actual Values. Setpoints can be read and written by a master com-
puter. Actual Values are read only. All Setpoints and Actual Values are stored as two byte values. That is, each register
address is the address of a two-byte value. Addresses are listed in hexadecimal. Data values (Setpoint ranges, increments,
and factory values) are in decimal.
Many Modbus communications drivers add 40001d to the actual address of the register addresses. For example: if
address 0h was to be read, 40001d would be the address required by the Modbus communications driver; if
address 320h (800d) was to be read, 40801d would be the address required by the Modbus communications driver.
6.3.2 USER-DEFINABLE MEMORY MAP AREA
The 489 contains a User Definable area in the memory map. This area allows remapping of the addresses of all Actual Val-
ues and Setpoints registers. The User Definable area has two sections:
1. A Register Index area (memory map addresses 0180h to 01FCh) that contains 125 Actual Values or Setpoints register
addresses.
2. A Register area (memory map addresses 0100h to 017Ch) that contains the data at the addresses in the Register
Index.
Register data that is separated in the rest of the memory map may be remapped to adjacent register addresses in the User
Definable Registers area. This is accomplished by writing to register addresses in the User Definable Register Index area.
This allows for improved throughput of data and can eliminate the need for multiple read command sequences.
For example, if the values of Average Phase Current (register addresses 0412h and 0413h) and Hottest Stator RTD Tem-
perature (register address 04A0h) are required to be read from an 489, their addresses may be remapped as follows:
1. Write 0412h to address 0180h (User Definable Register Index 0000) using function code 06 or 16.
2. Write 0413h to address 0181h (User Definable Register Index 0001) using function code 06 or 16.
(Average Phase Current is a double register number)
3. Write 04A0h to address 0182h (User Definable Register Index 0001) using function code 06 or 16.
A read (function code 03 or 04) of registers 0100h (User Definable Register 0000) and 0101h (User Definable Register
0001) will return the Average Phase Current and register 0102h (User Definable Register 0002) will return the Hottest Sta-
tor RTD Temperature.
6.3.3 EVENT RECORDER
The 489 event recorder data starts at address 3000h. Address 3003h is the ID number of the event of interest (a high num-
ber representing the latest event and a low number representing the oldest event). Event numbers start at zero each time
the event record is cleared, and count upwards. To retrieve event 1, write ‘1’ to the Event Record Selector (3003h) and read
the data from 3004h to 30E7h. To retrieve event 2, write ‘2’ to the Event Record Selector (3003h) and read the data from
3004h to 30E7h. All 40 events may be retrieved in this manner. The time and date stamp of each event may be used to
ensure that all events have been retrieved in order without new events corrupting the sequence of events (event 0 should
be less recent than event 1, event 1 should be less recent than event 2, etc.).
If more than 40 events have been recorded since the last time the event record was cleared, the earliest events will not be
accessible. For example, if 100 events have been recorded (i.e., the total events since last clear in register 3002h is 100),
events 60 through 99 may be retrieved. Writing any other value to the event record selector (register 3003h) will result in an
“invalid data value” error.
Each communications port can individually select the ID number of the event of interest by writing address 3003h. This way
the front port, rear port and auxiliary port can read different events from the event recorder simultaneously.
NOTE