Dixell XR77CX

Refrigeration controller

The Dixell XR77CX controls the compressor, fan, defrost and light of a low temperature cabinet or cold room, with an optional clock for scheduled defrosts. Its built-in RS485 line makes it compatible with EpiSensor Edge over Modbus RTU through a ZMB Modbus interface, with no converter. EpiSensor's Modbus profile reads the room probe, setpoint and differential.

  • Modbus RTU

Refrigeration controller

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Compatibility

Compatible with EpiSensor Edge over Modbus RTU through a ZMB Modbus interface

Dixell documents a built-in RS485 serial line on the XR77CX for a Modbus RTU monitoring system, with the address set by parameter Adr. A ZMB-31 or ZMB-30 on that line reads the controller and sends the values to the Gateway running Edge. The addresses come from EpiSensor's Modbus profile for the XR77CX.

Set Adr to a unique address first. Dixell's manual prints no register table, so compare the room probe with the display once, and record the parameter table code the controller reports as Ptb. Setpoint and parameter writes stay with the refrigeration contractor.

Connect it with

For any XR77CX: the RS485 line is on the controller's own terminals

  • Modbus
  • Wireless
  • Edge
  • Platforms
Refrigeration controller
Interface
Gateway
Edge
Output
XR77CXXR77CX RS485 terminals (+ and -)
ZMB-31Modbus RTU to the EpiSensor wireless network
ZGW-20 GatewayHosts Edge locally
EpiSensor EdgeModbus client + register map
Customer platformMQTT · API · files
Modbus RTU · RS-485
EpiSensor wireless
Runs locally
Optional onward data
Wire the controller's RS485 + and - terminals to the ZMB with shielded twisted pair. Set the ZMB to 9600 bit/s, 8 data bits, no parity and 1 stop bit and poll the controller's Adr address. Several XR controllers can share one bus at different addresses. The customer-platform output is optional; Edge remains the local system of record.

Specifications

Dixell's manual describes the XR77CX as a 32 x 74 mm microprocessor controller for low temperature ventilated refrigerating units with four relays, an optional real time clock with up to six daily defrosts split into workdays and holidays, and a day and night function with two setpoints.1

Power supply
24 Vac ±10 %, 12 to 40 Vdc ±10 %, 110 Vac or 230 Vac, 50/60 Hz, by model; 3 VA max1
Probe inputs
Up to 4 NTC or PT1000 probes, set by PbC1
Measuring range
NTC -40 to 110 °C; PT1000 -100 to 150 °C1
Accuracy and resolution
±0.7 °C ±1 digit at 25 °C ambient; 0.1 °C, 1 °C or 1 °F selectable1
Relay outputs
Compressor SPST 8(3) A or 16 A; defrost SPDT 8(3) A; fan SPST 5 A; aux SPDT 8(3) A, 250 Vac1
Serial line
Built-in RS485 for Modbus RTU; address Adr 1 to 247, default 11
Housing and protection
32 x 74 mm front, 60 mm deep, 71 x 29 mm panel cut-out; IP20, IP65 front1
Operating conditions
0 to 55 °C, 20 to 85 % RH non-condensing; clock back-up 24 hours1

Interface

This register map is for the XR77CX. XR75CX has its own interface and is not covered here.

Communication settings

Protocol
Modbus RTU on the built-in RS485 terminals (16 +, 17 -)
Unit address
Parameter Adr, 1 to 247, default 1
Baud rate
9600 bit/s
Data bits, parity and stop bits
8 data bits, no parity, 1 stop bit
Read with
FC03 (holding registers)
Addresses
Zero-based PDU addresses, as sent on the bus
Route into Edge
ZMB-31 or ZMB-30 on the RS485 terminals at 9600 bit/s 8N1. Any ZMB reads the three starter points; the ZMB-30 also adds its own waterproof probe.

From EpiSensor Modbus profile for the Dixell XR77CX4.

Register map

Download
PointAddressHexFormatScaleUnit
Room probe P1 256 0x0100 INT16 ×0.1 °C
Differential Hy 769 0x0301 UINT16 ×0.1 °C
Setpoint 882 0x0372 INT16 ×0.1 °C

Download the XR77CX register map as CSV

Assessment

XR77CX on its built-in RS485 line, read with EpiSensor's Modbus profile. Relay, alarm, door and clock states are outside this starter map.

InteroperabilitySupported with conditions
Dixell documents Modbus RTU on built-in RS485. The register addresses come from EpiSensor's profile, not a published Dixell table, and depend on the map code.14
AccuracySupported with conditions
Dixell states ±0.7 °C ±1 digit and 0.1 °C resolution with NTC or PT1000 probes. The room probe is placed for control.1
SecurityNot yet assessed
The manual describes a keyboard lock but no protection on the serial line.1
ReliabilitySupported with conditions
The RS485 line is on the controller's own terminals, and the manual lists probe failure and clock alarms. Edge timestamps each read, so a lost bus shows as missing data.1
RuggednessSupported with conditions
IP65 front and IP20 body, rated 0 to 55 °C.1
ScalabilityWell supported
Built-in RS485 with addresses from 1 to 247 lets several controllers share one bus without converters.1
LifecycleSupported with conditions
Copeland still hosts the XR77CX manual. The controller reports its parameter table code as Ptb, so record it with the firmware.13

Edge template

This JSON file supplies the register map. Applying it to an existing meter replaces its sensor list while retaining the site connection, unit ID and enable state.

ModelConnectionPointsVersionUpdatedDownload
XR77CX Built-in RS485, Modbus RTU, address Adr, 1 to 247, default 1 3 1.0.0 Download

Downloads need a signed-in account with Edge download access.

Use the template in Edge

  1. Import the JSON file

    In Edge, open Settings, then Devices and Templates. Choose Import JSON and select the downloaded file. Confirm that the model and template name match your device.

  2. Load the map for your meter

    For a new Modbus device, use Load Template before entering the manufacturer or model; it fills those fields and the register list. Set the name, site connection and unit ID, check the polling enable state, then test before saving. For an existing device, apply only to the matching model; this replaces its sensor list but retains its connection, unit ID and enable state.

  3. Test a reading

    Use Test in the wizard and compare a known reading with the meter display. Check its unit, sign and scale, then confirm that timestamps keep advancing. These starter maps are read-only and leave exports off until you configure them.

Setup

Read the room probe

EpiSensor's Modbus profile places the XR77CX room probe at holding register 256 (0x0100) as a signed value in tenths of a degree.

Request PDU
03 01 00 00 01
Address
256 decimal = 0x0100, zero-based, one register
Decode
Signed 16-bit, divide by 10 with rES = dE: a synthetic reply of FF 06 is -250, which is -25.0 °C
Compare with
The XR77CX display, which shows the room probe by default

Acceptance: Accept the map when the room probe agrees with the display. The reply bytes are an example, not a captured reply. If nothing answers, check Adr, the + and - polarity and 9600 bit/s.

  1. Set the address

    Set Adr (1 to 247) to a unique address for the bus and note Ptb, the parameter map code. Check rES: the tenths decode applies with rES = dE in °C.

  2. Wire the RS485 terminals to the ZMB

    Connect the controller's RS485 + and - to the ZMB with shielded twisted pair, terminate both ends, and set the ZMB to 9600 bit/s, 8 data bits, no parity, 1 stop bit.

  3. Read the room probe once

    Read holding register 256 (0x0100) with FC03 and divide by 10. Compare it with the display.

  4. Add the setpoint and differential

    Read the setpoint at 882 (0x0372) and Hy at 769 (0x0301). If the setpoint does not match SEt on the controller, leave it out and confirm the map for the reported Ptb.

  5. Place the record probe

    Fit an independent probe at the warmest product position and set Edge alarm limits and delays to the site's HACCP plan.

Common questions

Does the XR77CX need a converter for Modbus?
No. The XR77CX has a built-in RS485 line for a Modbus RTU monitoring system. Wire it straight to the ZMB.1
Where do the register addresses come from?
From EpiSensor's Modbus profile for the XR77CX. Dixell's manual prints no register table, so compare the room probe with the display before saving the map.14
Why might the setpoint read a different value?
Dixell's manual lists Ptb, a read-only parameter map code, and the parameter registers follow that map. Record Ptb and compare the setpoint read with SEt on the controller before keeping it.1
Can one ZMB read several XR77CX controllers?
Yes, each at its own Adr. The starter map takes three registers per controller, and a ZMB reads 8 or more registers, up to 16 or more depending on the model.15

Sources

  1. XR77CX installing and operating instructions 1592020620 r1.0, 23.03.2015 (opens in a new tab) (PDF) Dixell (Copeland)
  2. XR75CX installing and operating instructions 1592020610 r1.0, 27.03.2015 (opens in a new tab) (PDF) Dixell (Copeland)
  3. Dixell brand page (opens in a new tab) Copeland
  4. EpiSensor Modbus profile for the Dixell XR77CX (opens in a new tab) EpiSensor
  5. ZMB-3X Modbus interface datasheet EPI-195-00 (opens in a new tab) (PDF) EpiSensor

Further reading

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