Appendix B: Modbus Communication

Communication protocol

The exchange between PC and OM-310 is effected via data packages.

Data packet format (Table 2.1)

Field	Description
START	Silence interval – over 2 ms at 9600 baud, or over 4 ms at 19200 baud
ADDRESS ID	OM-310 communication address (8 bit)
FUNCTION	Command code (8 bit)
DATA 0 … DATA (n-1)	Data contents: N×8 data bit (n≤24)
CRC CHK low	CRC checksum (16 bits) – low byte
CRC CHK high	CRC checksum (16 bits) – high byte
END	Silence interval – over 2 ms at 9600 baud, or over 2 ms at 19200 baud

CMD (command code) and DATA (data symbols)

Data symbols format depends on command codes.

Command code 0x03 – n-words read

Example: Read 2 continuous words from address 0x64 (100) in OM-310 with communication address 0x01.

Command message		Response message
ADDRESS ID	0x01	ADR	0x01
FUNCTION	0x03	CMD	0x03
Start data address	0x00, 0x64	Data amount, bytes	0x04
Data amount in words	0x00, 0x02	Data contents	0x17, 0x70
CRC CHK low	0x85	Data contents	0x00, 0x00
CRC CHK high	0xD4	CRC CHK low	0xFE
		CRC CHK high	0x5C

Command code 0x06 – write (record) one word

WARNING

Using this command is not recommended as writing incorrect data may lead to OM-310 failure.

Data writing is possible only to the programmable parameter’s addresses (Table 1.5), except for the following parameters:

Parameter	Code	Address
Equipment operation time counter, days	tbU	191
User access code	LOC	192
Service engineer access code	PA5	193
System reset to factory settings	PPP	194
Device version	rEL	200

Parameter writing is performed independently from the installed Service Engineer protection (the entry made via communication line has a higher priority).

When a new parameter value is written into a MMSP-protected cell, such parameter will automatically be excluded from this mode.

Command code 0x08 – diagnostics

0x08 function provides a number of tests for checking communication system between PC and OM-310, and for OM-310 integrity control.

The function uses the sub function field to specify the action performed (test).

Sub function 0x00 – query data response

Data transferred in the query field must return in the response data field.

Example: sub function 0x00 request and response in OM-310 with communication address 0x01.

Command message		Response message
ADDRESS ID	0x01	ADR	0x01
FUNCTION	0x08	CMD	0x08
Subfunction	0x00, 0x00	Subfunction	0x00, 0x00
Data	0xA0, 0x3C	Data	0xA0, 0x3C
CRC CHK low	0x98	CRC CHK low	0x98
CRC CHK high	0x1A	CRC CHK high	0x1A

Sub function 0x01 – communication options restart

OM-310 peripheral port shall be initialized and restarted.

Example: sub function 0x01 request (response is not returned) for OM-310 with communication address 0x01.

Command message
ADDRESS ID	0x01
FUNCTION	0x08
Subfunction	0x00, 0x01
Data	0x00, 0x00
CRC CHK low	0xB1
CRC CHK high	0xCB

CRC – Cyclic redundancy check code

The checksum (CRC16) is a cyclic redundancy check code based on 0xA001 polynomial. The transmitting device forms the checksum for all bytes of the message transmitted. The receiving device similarly forms the checksum for all bytes of the message received, and compares it to the checksum received from the transmission device. When received and transmitted checksums do not match, an error message is generated.

The checksum field size occupies two bytes. The checksum within message is transferred with low byte coming first.

The checksum is registered under the following algorithm:

1. Load CRC register (16 bit) with units (0xFFFF)
2. Exclusive OR with first 8 bytes of message and CRC register contents
3. Offset the result one bit to the right
4. If the offset bit = 1, the exclusive OR of the register contents with 0xA001 value
5. If the offset bit = 0, repeat step 3
6. Repeat steps 3, 4, 5 until 8 offsets have been completed
7. Exclusive OR with the next 8 bits of the message byte and CRC register contents
8. Repeat steps 3–7 until all bytes of the message have been processed
9. The finite register contents will contain the checksum

CRC code generation example in C:

unsigned int crc_chk(unsigned char* data, unsigned char length) {
    int j;
    unsigned int reg_crc = 0xFFFF;
    while(length--) {
        reg_crc ^= *data++;
        for(j = 0; j < 8; j++) {
            if(reg_crc & 0x01)
                reg_crc = (reg_crc >> 1) ^ 0xA001;  // LSB(b0)=1
            else
                reg_crc = reg_crc >> 1;
        }
    }
    return reg_crc;
}

Communication error handling

When an error situation occurs at time of a frame receipt (parity error, frame error, checksum error), the OM-310 device does not return a response.

When an error occurs in the format or in the value of the data transferred (unsupported function code, etc.), OM-310 receives the request frame and forms a response with the error indicator and code. A high-order function field bit inserted in the unit serves as error indicator.

Example: function 0x30 error response (illegal function) from OM-310 with communication address 0x01.

Command message		Response message
ADDRESS ID	0x01	ADR	0x01
FUNCTION	0x30	FUNCTION ERROR	0xB0
DATA	…	Error code	0x01
CRC CHK low	…	CRC CHK low	0x94
CRC CHK high	…	CRC CHK high	0x00

Table 2.6 – Error codes

Error code	Title	Description
0x01	ILLEGAL FUNCTION	Function code received cannot be processed by OM-310
0x02	ILLEGAL DATA ADDRESS	Data address in the query is not accessible by the given subordinate
0x03	ILLEGAL DATA VALUE	Value contained in the request data field is not a valid value for OM-310
0x04	SLAVE DEVICE FAILURE	While OM-310 attempted to perform the requested action, an unrecoverable error occurred
0x05	ACKNOWLEDGE	OM-310 accepted request and is processing it, but it requires a long time
0x06	SLAVE DEVICE BUSY	OM-310 is busy with command processing. Master must repeat message later
0x07	NEGATIVE ACKNOWLEDGE	OM-310 cannot perform the program function received in the request

Measured and Displayed Parameters (Table 1.4)

Currents

Measurement function	Range	Accuracy	Mnemonics	Address	Units
Phase currents RMS (built-in CT)	0.5–100	2%	iF1, iF2, iF3	100, 101, 102	1/10 A
Phase currents RMS (built-in CT)	100–300	5%	iF1, iF2, iF3	100, 101, 102	1/10 A
Phase currents RMS (external CT)	5–999	2%	iF1, iF2, iF3	100, 101, 102	1/10 A
Zero sequence current RMS, A	0.3–9.9	2%	iF0	103	1/10 A
Average current value per phase	—	—	iS1, iS2, iS3	104, 105, 106	1/10 A
Max average current value per phase	<3 Itt	2%	in1, in2, in3	107, 108, 109	1/10 A
Max average current value per phase	>3 Itt	10%	in1, in2, in3	107, 108, 109	1/10 A
Negative sequence current (imbalance), A	0.2–200	5%	ioP	110	1/10 A

Note

All average values can be reset with RES/MEM/SEL button at time of max average current value output for any phase (real-time average current value for corresponding phase is assigned).

Voltages

Measurement function	Range	Accuracy	Mnemonics	Address	Units
Phase voltages RMS (with zero wire), V	100–300	3 V	UF1, UF2, UF3	111, 112, 113	Volts
Line voltage RMS values, V	100–450	5 V	UL1, UL2, UL3	114, 115, 116	Volts
Positive-sequence voltage, V	100–300	3 V	UPP	117	Volts
Negative-sequence voltage, V	3–300	3 V	UoP	118	Volts
Zero-sequence voltage, V	3–100	3 V	UnP	119	Volts

Note

Zero-sequence voltage (vector sum of three phase voltages, divided by three) measurement is possible only when zero wire is connected to OM-310.

Power and Cosines

Measurement function	Range	Accuracy	Mnemonics	Address	Units
Gross power, kVA	0–5000	5%	Pot	120, 121	W × 10
Active power, kW	0–5000	5%	PoR	122, 123	W × 10
Reactive power, kVAr	0–5000	5%	PoJ	124, 125	W × 10
Phase L1 active power, kW	0–5000	5%	PAR	126, 127	W × 10
Phase L2 active power, kW	0–5000	5%	PAb	128, 129	W × 10
Phase L3 active power, kW	0–5000	5%	PAC	130, 131	W × 10
Phase L1 cos φ	0.00–1.00	5%	PCA	132	×1000
Phase L2 cos φ	0.00–1.00	5%	PCb	133	×1000
Phase L3 cos φ	0.00–1.00	5%	PCC	134	×1000

Note

If power consumed by the load is over 999 kW (kVA, kVAr), then MW (MVA, MVAr) is displayed on screen with a “п”-shaped point in the middle position. For instance, if the display shows “3п4”, it means 3.4 MW (MVA, MVAr).

Timers and Frequency

Measurement function	Range	Accuracy	Mnemonics	Address	Units
Time before load disconnect (power exceeded), sec	0–600	1s	tOP	135	seconds
Time before AR delay termination, sec	0–900	1s	tAP	136	seconds
Wait time after de-energizing (over wattage), min	0–30	1s	ttP	137	seconds
Mains frequency, Hz	45–65	1%	FFF	138	1/10 Hz

Note

• If the time is not defined, ”---” is displayed on screen
• If automatic reset is forbidden, “not” message is displayed

Energy Meters

Measurement function	Range	Accuracy	Address	Units
Active electric power, phase L1, kWh	0–200,000,000	5%	90, 91	100s of Wh
Active electric power, phase L2, kWh	0–200,000,000	5%	92, 93	100s of Wh
Active electric power, phase L3, kWh	0–200,000,000	5%	94, 95	100s of Wh

Note

• When working with external transformers of rated current over 100A, the currents (measured and calculated), except for the zero sequence current (ground fault) are transferred via RS-232/RS-485 in amperes
• In excess of the energy meter value 200,000,000, the counter is reset and energy metering will start from zero
• Recording the current values of the energy in the non-volatile memory is performed every 15 min

Programmable Parameters (Table 1.5)

Transformers

Parameter	Code	Min	Max	Default	Description	Address
CT in use	tPt	0	1	0	0 = integrated CT, 1 = external CT	150
CT rated current, A	tnt	20	800	100	For external CT	151
Load rated current, A	ind	5	700	10	Used for calculating current and time of overcurrent protection	152

Power Control

Parameter	Code	Min	Max	Default	Description	Address
Rated power of load, kW	Pnn	3	450	5	—	153
Power limiter threshold calculation	rPn	0	2	0	0 = per phase (Pnn/3), 1 = per phase +20%, 2 = aggregate	154
Main threshold, %	P1F	50	150	110	—	155
Additional threshold, %	P2F	30	100	90	—	156
Time before load relay de-energizing (main), sec	t1n	0	300	60	Time before load disconnect when main threshold exceeded	157
Time while load relay is open (main), min	t1F	1	60	5	Time relay stays open after main threshold trip	158
Time before characterizing relay de-energizing, sec	t2n	0	300	10	Additional threshold delay	159
Time while characterizing relay is open, min	t2F	1	60	5	Time relay stays open after additional threshold trip	160
Additional threshold for characterizing relay closure, %	P2n	3	100	30	Threshold for relay closure after overload	161
Characterizing relay operation mode	rr5	0	4	0	0=alarm, 1=time relay, 2=additional load, 3=reactive power alarm, 4=active power alarm	162
Characterizing relay activation mode (when rr5=2)	r2r	0	2	0	0=after time t2F, 1=after power reduction, 2=first event	163
Delay of characterizing relay closure, sec	t12	0	300	5	Relative to load relay closure	164
Allowable load wattless power, kVAr	Prn	3	450	5	—	165

Current Protection - Maximum Current

Parameter	Code	Min	Max	Default	Description	Address
Maximum current protection type	i=P	0	5	0	0=independent, 1=SIT, 2=VIT, 3=EIT, 4=UIT, 5=RI	166
Max current protection tripping ratio	i=5	0.8	9.0	2.0	Ratio to load rated current (when i=P=0)	167
Current protection tripping delay, sec	i=t	0.3	600	10.0	—	168
Protection function permission	i=r	0	2	0	0=prohibited, 1=permitted (no AR), 2=permitted (with AR)	169

Current Protection - Ground Fault (iF0)

Parameter	Code	Min	Max	Default	Description	Address
Current fault tripping setting, A	i_5	0.3	5.0	0.5	—	170
Protection tripping delay, sec	i_t	0.3	2.0	1.0	—	171
Protection function permission	i_r	0	2	0	0=prohibited, 1=permitted (no AR), 2=permitted (with AR)	172

Voltage Protection

Parameter	Code	Min	Max	Default	Description	Address
Minimum line voltage, V	U_5	270	415	320	—	173
Min voltage tripping delay, sec	U_t	5	30	10	—	174
Min voltage protection permission	U_r	0	2	0	0=prohibited, 1=permitted (no AR), 2=permitted (with AR)	175
Maximum line voltage, V	U¯5	330	475	415	—	176
Max voltage tripping delay, sec	U¯t	1	10	2	—	177
Max voltage protection permission	U¯r	0	2	0	0=prohibited, 1=permitted (no AR), 2=permitted (with AR)	178
Line voltage imbalance, V	Un5	15	120	35	—	179
Imbalance tripping delay, sec	Unt	1	30	5	—	180
Imbalance protection permission	Unr	0	2	0	0=prohibited, 1=permitted (no AR), 2=permitted (with AR)	181
Phase sequence protection permission	UЧr	0	2	0	0=prohibited, 1=permitted (no AR), 2=permitted (with AR)	182

Load Engagement and Automatic Reset

Parameter	Code	Min	Max	Default	Description	Address
Automatic reset (AR) time, sec	Att	0	900	5	—	183
AR prohibited for all faults	Arr	0	1	1	0=prohibited, 1=permitted (except voltage faults)	184
Load relay after power-on	APd	0	2	1	0=manual, 1=after AR delay, 2=after 2 sec	185
Load start/cutoff from front panel	ACd	0	3	0	0=prohibited, 1=energize, 2=de-energize, 3=both	186

Miscellaneous

Parameter	Code	Min	Max	Default	Description	Address
Average current measurement time, sec	t5i	10	600	60	Time for measuring iS1, iS2, iS3	187
MMSP mode enable	5in	0	1	1	0=disabled, 1=enabled	188
Indication before load energize	5iP	0	2	1	0=UAb, 1=PoA, 2=Att countdown	189
Parameter indication mode	5iC	0	1	1	0=continuous, 1=15 sec then iF1	190
Equipment operation time, days	tbU	0	999	0	Read-only; hours via Modbus	191
User access code	LOC	0	9	0	0=unlocked, 1-9=password	192
Service engineer access code	PA5	000	999	123	000=permitted, other=password	193
System reset to factory settings	PPP	0	1	0	Set 1 to restore defaults	194

Serial Interface Parameters (RS-485/RS-232)

Parameter	Code	Min	Max	Default	Description	Address
Communication address	r5A	1	247	1	—	195
Transfer rate	r55	0	1	0	0=9600, 1=19200 baud	196
Response to loss of connection	r5P	0	3	0	0=continue, 1=warning, 2=warning+de-energize (AR), 3=warning+de-energize (no AR)	197
Response timeout detection, sec	r50	0	120	0	0=prohibited	198
Communication permitted	rPP	0	2	0	0=prohibited, 1=RS-232, 2=MODBUS	199
Device version	rEL	—	—	14	Read-only; firmware dependent	200
Remote control via RS-232/RS-485	dUd	0	2	0	0=prohibited, 1=permitted, 2=wait for command	201
Remote control via switch	dUc	0	4	0	0=prohibited, 1-4=see manual	202
Starter monitoring	CCi	0	1	0	0=off, 1=on	203

Status and Fault Registers

OM Status Register (Address 240)

Bit	Description
0	0 = no fault, 1 = fault (code in registers 241, 242)
1	0 = load relay open, 1 = load relay closed
2	0 = characterizing relay open, 1 = characterizing relay closed
3	0 = restart not activated, 1 = AR expected
4-6	Characterizing relay mode: 000=alarm, 001=time relay, 010=additional load, 011=reactive power alarm
7	0 = MMSP disabled, 1 = MMSP enabled

Fault Registers

Register	Address	Description
Fault register 1	241	Bit mapping per Table 2.8 (0=no fault, 1=fault)
Fault register 2	242	Bit mapping per Table 2.8

Fault codes (Table 2.8)

Fault description	Mnemonic	Parameter value	Address	Fault code	Register bit
De-energizing based on main threshold crossing	AP=	Main threshold value in 100×W	300	0	241:0
Additional threshold crossing	APd	Additional threshold value in 100×W	301	1	241:1
Maximum phase current fault	Ai=	Maximum phase current	302	2	241:2
Line-to-earth fault (zero sequence current)	Ai_	Zero sequence current	303	3	241:3
Currents present when load relay is de-energized (contactor fault)	ACo	Current	304	4	241:4
Phase sequence order fault	AU	—	—	5	241:5
Minimum line voltage fault	AU_	Voltage	306	6	241:6
Maximum line voltage fault	AU¯	Voltage	307	7	241:7
Phase imbalance fault	AUn	Imbalance	308	8	241:8
Remote control channel fault	AdU	—	—	9	241:9
Emergency load de-energize, AR not possible	EAd	—	—	10	241:10
Emergency de-energize of load, AR possible by pressing UP+DOWN	EOd	—	—	11	241:11
Emergency load de-energizing by remote breaker	Edc	—	—	12	241:12
EEPROM destruction	EEP	—	—	13	241:13

Fault Log Registers

Description	Address
Fault code 1	243
Parameter value 1	244
Fault time 1 (high word)	245
Fault time 1 (low word)	246
Fault code 2	247
Parameter value 2	248
Fault time 2 (high word)	249
Fault time 2 (low word)	250
Fault code 3	251
Parameter value 3	252
Fault time 3 (high word)	253
Fault time 3 (low word)	254
Fault code 4	255
Parameter value 4	256
Fault time 4 (high word)	257
Fault time 4 (low word)	258
Fault code 5	259
Parameter value 5	260
Fault time 5 (high word)	261
Fault time 5 (low word)	262

Note

• Fault time is measured in minutes since OM-310 power-on
• Upon delivery or after factory reset, error code 40 and parameter value 10000 are written in the log
• When power is supplied, the number 5000000 is entered in all fault time registers

Fault Parameter Value Registers

Description	Address
Main threshold value (100×W)	300
Additional threshold value (100×W)	301
Maximum phase current	302
Zero sequence current	303
Contactor fault current	304
Minimum voltage fault value	306
Maximum voltage fault value	307
Imbalance fault value	308

Command Register

Register	Address	Values
R_COMMAND	220	0=de-energize, 1=normal operation, 2=early energize

Value	Action
0	De-energize load. If load is de-energized, before a power-on command from Remote Control has been received, the load will not energize. If load is energized, it will be de-energized.
1	Normal device operation. If load was de-energized by remote control command, by pressing DOWN+UP buttons (while ACd=3), or in case of a failure after which automatic restart is permitted, then load will be energized within specified automatic restart time.
2	Early load energizing. Value “2” record will lead to load power-on until expiration of the automatic reset time period. After load power-on, R_COMMAND=1.

The R_COMMAND value is regarded by the OM-310 operation algorithm when dUd=1 or dUd=2. If dUd=0 and the user sets dUd=1 or dUd=2, then 0 will be recorded to R_COMMAND.

If dUd=1, then after energizing “1” value (device normal operation) will be recorded in the command register.

If dUd=2, then after energizing “0” value (load de-energized until the command to energize is received) will be recorded in the command register.

In case of an emergency load shutdown by simultaneous pressing DOWN+UP buttons (while ACd=2 or ACd=3), the command register will be reset to 0.

Energy Meter Reset

Register	Address	Description
Energy reset	239	Write 1 to reset all energy meters; auto-resets to 0