2.2 Serial Data Communication
The UPS provides an RJ45 RS485 interface based on the ModBUS protocol. It sends protocol commands to the battery pack to obtain detailed operational status, SOC, SOH, and other critical parameter information for protection coordination.

Interface Definition
Pin Definition
Pin 1: 485A
Pin 2: 485B
Pins 3-8: Reserved

The lithium battery UPS interfaces with the lithium battery pack via an RS485 communication port, supporting the standard MODBUS RTU protocol. The UPS communication interface acts as the master, while the battery pack (BMS) functions as the slave. The UPS reads BMS data from the battery pack to determine UPS actions. For battery packs with multiple modules in parallel, a master host is required to coordinate the entire battery system. This host determines whether the pack can continue discharging or charging, integrates data to calculate total capacity and remaining power, etc. The UPS communicates only with the host, executing charge/discharge actions based on host instructions. The host address is fixed at 01, meaning the UPS reads data only from the battery pack at address 01.
In multi-module battery systems, the host must provide comprehensive information representing the entire battery bank's status externally. For example, the system only recognizes a discharge failure when all modules fail simultaneously, preventing power output. If any battery module triggers overvoltage or overtemperature protection and cannot be isolated from the system, the entire battery bank should cease charging.
The UPS uses the MODBUS 03 read query command. The starting register address must be 0x9000, reading 15 registers at a time.
Example: 01 03 90 00 00 0F CRC
The battery pack returns information where each field is 2 bytes long, as follows:
0x9000: Battery pack status, with possible values:
1--Fault status. Indicates overall system condition. For multi-module systems, this fault is reported only when the entire system cannot charge or discharge. If any module still supports discharge or the system can accept charging, it is not considered a system fault.
2--Low voltage, single module or system average SOC < 20%
3--Charging state
4--Discharge status
5--Full Energy State: Generally indicates no charging, no discharging, no low voltage, and no faults
0x9001, Battery Voltage, accuracy 0.1V. For parallel multi-battery module systems, the host reports the highest voltage during charging and the lowest battery module voltage during discharging.
0x9002, Charging Current, accuracy 0.1A. For parallel multi-module systems, reports total current.
0x9003, Discharge Current, accuracy 0.1A. For parallel multi-battery module systems, reports total current.
0x9004, Battery Capacity, unit defined by the 0x900A field. For parallel multi-battery module systems, reports the total capacity;
0x9005, SOC, remaining power percentage, accuracy 1%, reports average SOC for parallel multi-battery module systems;
0x9006, Discharge Duration, in minutes, precision 1. Reset timing after battery pack reset or host replacement;
0x9007, Remaining runtime, in minutes, with 1% precision;
0x9008, SOH (State of Health), battery lifespan percentage with 1% precision. For parallel multi-module systems, reports the lowest SOH module value;
0x9009, Battery Temperature, in degrees Celsius, precision 0.1OC. For parallel multi-module systems, reports the highest module temperature;
0x900A, Battery capacity unit:
0 -- mAh (for capacities below 65Ah)
1 - 0.1Ah (mandatory for capacities above 65Ah)
0x900B, Charging Dry Contact Flag: (Normal dry contact NO, protection is NC)
0 -- Dry contact inactive
1 -- Charging dry contact action ( ) , Stop charger charging
0x900C, Discharge Dry Contact Flag: (Normal dry contact NO, protective NC)
0 -- No action on dry contact
1 -- Discharge dry contact activated, stop discharging
0x900D, Reserved
0x900E, Reserved
CRC
If a field has no value, it may be filled with 0x20, 0x20
BMS response example: 01 03 1E 00 03 02 40 00 4C 00 00 03 E8 00 5C 04 28 00 44 00 64 01 43 00 01 00 01 00 00 20 20 20 20 CRC
Representing respectively:

    1. Status: 00 03, Charging status
         2. Battery voltage: 02 40 = 57.6V
         3. Charging current: 00 4C = 7.6A
         4. Discharge current:   00 00 = 0A
         5. Battery rated capacity: 03 E8 = 1000*0.1Ah=100Ah
         6. SOC:     00 5C = 92%
         7. Discharge Duration: 04 28 = 1064 minutes
         8. Remaining runtime: 00 44 = 68 minutes
         9. SOH: 00 64   = 100%
        10. Battery Temperature: 01 43 = 32.3 °C

11. Capacity unit: 00 01 = 0.1Ah
12. Charging dry contact: 00 01 Charging dry contact activated, stop charger charging
13. Discharge dry contact: 00 00 Discharge dry contact inactive, discharge permitted
14. Reserved, 20 20

15. Reserved, 20 20

    After receiving data via communication, the UPS applies the same logic as the dry contact signals for protection.
    For data not provided by the BMS, send 0x20 0x20 (two 0x20s).
    Serial communication serves as a secondary communication method to ensure reliable coordination.