119
$ 10 = function code (write multiple registers) $ 02 D3 Æ (1 bit offset) Æ $ 02 D4 Æ Write Access Password $ 00 08 = register count (8) $ 10 = byte count (16) $ 31 32 33 20 20 20 20 20 20 20 20 20 20 20 20 20 = data (“123”, followed by 13 spaces) Reply: $ 01 10 02 BB 00 08 xx xx $ 02 C3 Æ (1 bit offset) Æ $ 02 C4 Æ Write Access Password $ 00 08 = register count (8) Now we again repeat step 1 to verify the current security level. Reply: $ 01 03 02 00 00 xx xx This verifies that the SCADA password worked, and did indeed give us access to level 0 security. Notice that the level did not increase to 1 or 2 because we have a level 1 password set. If we were to enter the level 1 password, access level 2 would be granted because there is no level 2 password set. More notes on SCADA passwords Note that the SCADA password is stored as a numeric value. The password is rightjustified in the field shown on the EMCP 3 control panel, and left-justified when set/written over SCADA, but it is numerically the same (00000001 is the same as 1_______ -- 1 with seven spaces after it). Just as with any number, leading zeros get dropped, and trailing zeros are kept (so “01” is stored as “1”, but “10” is stored as “10”). Also, the first space terminates the string, so an entry of “12 3” (space between the 2 and the 3) will return an exception because only spaces (or nulls, after the first 8 bytes) are accepted after the first space. Setpoint Interpretation and Calculation This example lays out the method of reading and writing to setpoints, including the data conversion between the register data and engineering value. Let us consider Block # 1 Setpoint # 2, Low Engine Oil Pressure Warning Event Threshold. Reading the value, you may get: $ 00 A0 00 00 That corresponds to a decimal value of 655,360. Now look at the SCALING and divide by 212 to get a decimal value of 360. The current setpoint for Low Engine Oil Pressure Warning Event Threshold is then 360 kPa. Now let’s say you would like to change that to 327.8 kPa. First, check the RESOLUTION, and you will find that the setpoint will be rounded to the nearest 1 kPa. Therefore, we might as well round the value ourselves. We round it to 328 kPa.
