MODBUS.md

Modbus

The Sequent Microsystems Four Relays four HV Inputs 8-Layer Stackable HAT for Raspberry Pi V 4.0 or higher can be accessed thru Modbus RTU protocol over RS-485 port. You can set-up the RS-485 port with 4rel4in command.

Example:

~$ 4rel4in 0 cfg485wr 1 9600 1 0 1

Set Modbus RTU , Baudrate: 9600bps, 1 Stop Bit, parity: None, slave address base: 1

~$ 4rel4in -h cfg485wr

display the full set of options

Slave Address

The three address jumpers have a dual purpose. When the card is accessed from Raspberry Pi, the jumpers define the offset of the I2C address, permitting stacking of up to 8 cards. When the card is accessed through MODBUS protocol over the RS485 port, the jumpers define the offset of the RS485 base address set by the software.

Modbus object types

All modbus RTU object type with standard addresses are implemented : Coils, Discrete Inputs, Input registers, Holding registers.

Coils

Acces level Read/Write, Size 1 bit

Device function	Register Address	Modbus Address	Description
RELAY1	0001	0x00	Relay #1 control
RELAY2	0002	0x01	Relay #2 control
RELAY3	0003	0x02	Relay #3 control
RELAY4	0004	0x03	Relay #4 control
LED1_MAN	0005	0x04	LED1 control type (0 copy the input state/ 1 manual)
ED2_MAN	0006	0x05	LED2 control type
LED3_MAN	0007	0x06	LED3 control type
LED4_MAN	0008	0x07	LED4 control type
LED1	0009	0x08	LED1 turn coil
LED2	0010	0x09	LED2 turn coil
LED3	0011	0x0a	LED3 turn coil
LED4	0012	0x0b	LED4 turn coil
IN1_COUNT_ENABLE	0013	0x0c	Counter enable on input #1
IN2_COUNT_ENABLE	0014	0x0d	Counter enable on input #2
IN3_COUNT_ENABLE	0015	0x0e	Counter enable on input #3
IN4_COUNT_ENABLE	0016	0x0f	Counter enable on input #4
ENCODER1_ENABLE	0017	0x10	Encoder enable on inputs #1/2
ENCODER2_ENABLE	0018	0x011	Encoder enable on inputs #3/4

Discrete Inputs

Access level Read Only, Size 1 bit

Device function	Register Address	Modbus Address	Description
IN_1	10001	0x00	input #1 state
IN_2	10002	0x01	input #2 state
IN_3	10003	0x02	input #3 state
IN_4	10004	0x03	input #4 state
AC_IN_1	10005	0x04	filtred input #1 state (sense AC signals)
AC_IN_2	10006	0x05	filtred input #2 state
AC_IN_3	10007	0x06	filtred input #3 state
AC_IN_4	10008	0x07	filtred input #4 state
BUTTON	10008	0x07	Push button state

Input registers

Access level Read Only, Size 16 bits

Device function	Register Address	Modbus Address	Measurement Unit	Description
COUNT1_L	30001	0x00		Input #1 low 16bits value
COUNT1_H	30002	0x01		Input #1 high 16bits value
COUNT2_L	30003	0x02		Input #2 low 16 bits value
COUNT2_H	30004	0x03		Input #2 high 16bits value
COUNT3_L	30005	0x04		Input #3 low 16bits value
COUNT3_H	30006	0x05		Input #3 high 16bits value
COUNT4_L	30007	0x06		Input #4 low 16bits value
COUNT4_H	30008	0x07		Input #4 high 16bits value
PPS1	30009	0x08	Hz	Input #1 conts per second
PPS2	30010	0x09	Hz	Input #2 conts per second
PPS3	30011	0x0a	Hz	Input #3 conts per second
PPS4	30012	0x0b	Hz	Input #4 conts per second
ENC_VAL1_L	30013	0x0c		Encoder #1 counter low 16bits
ENC_VAL1_H	30014	0x0d		Encoder #1 counter high 16bits
ENC_VAL2_L	30015	0x0e		Encoder #2 counter low 16bits
ENC_VAL2_H	30016	0x0f		Encoder #2 counter high 16bits
PWM1_FILL	30017	0x10	%/100	Fill factor for PWM input on channel 1
PWM2_FILL	30018	0x11	%/100	Fill factor for PWM input on channel 2
PWM3_FILL	30019	0x12	%/100	Fill factor for PWM input on channel 3
PWM4_FILL	30020	0x13	%/100	Fill factor for PWM input on channel 4
PWM1_FREQ	30021	0x14	Hz	Frequency for PWM input on channel 1
PWM2_FREQ	30022	0x15	Hz	Frequency for PWM input on channel 1
PWM3_FREQ	30023	0x16	Hz	Frequency for PWM input on channel 1
PWM4_FREQ	30024	0x17	Hz	Frequency for PWM input on channel 1

Holding registers

Access level Read/Write, Size 16 bits

Device function	Register Address	Modbus Address	Measurement Unit	Range	Description
RESET_COUNT_CHANNEL	40001	0x00		1..4	Reset counter for specified input number
HR_RESET_ENCODER_CHANNEL	40002	0x01		1..2	Reset counter for specified Encoder number

Function codes implemented

• Read Coils (0x01)
• Read Discrete Inputs (0x02)
• Read Holding Registers (0x03)
• Read Input Registers (0x04)
• Write Single Coil (0x05)
• Write Single Register (0x06)
• Write Multiple Coils (0x0f)
• Write Multiple registers (0x10)