Meta Description
Official communications reference document (Doc No. 10-40280 Rev., December 2019) covering Anafaze/AB and Modbus® RTU serial communication protocols, data mapping, register tables, and parameter definitions for Watlow CLS200 loop controllers, MLS300 multi-loop units, and CAS200 alarm scanners.
Document Overview
This official communications specification (Document 10-40280, Released December 2019) serves as the definitive programming reference for software developers, system integrators, and automation engineers interfacing Watlow CLS200 compact loop controllers, MLS300 multi-loop process units, and CAS200 alarm scanners via serial communication links.
The guide standardizes two industry-supported serial protocols: proprietary Anafaze/AB (Allen Bradley-compatible) and universal Modbus® RTU. It delivers full packet structures, error-check algorithms, complete data table mappings, and detailed parameter descriptions to enable seamless master-slave data exchange between host PCs, PLCs, HMIs, and Watlow process hardware. All technical content strictly follows Watlow’s factory official engineering data and firmware definitions.
Supported Device Families
CLS200 Series: CLS204 (4-loop), CLS208 (8-loop), CLS216 (16-loop) compact PID temperature controllers
MLS300 Series: MLS316, MLS332 multi-loop process control units
CAS200: Dedicated alarm scanner module for multi-channel process monitoring
Core Communication Hardware Interface
All three product lines share identical serial physical layer standards:
Physical Bus: EIA/TIA-232 (point-to-point) or EIA/TIA-485 (multi-drop network)
Selectable Baud Rates: 2400, 9600, 19200 bps
Serial Frame Format: 8 data bits, no parity, 1 or 2 stop bits
Network Topology: Master-slave half-duplex architecture (controller acts as slave; only host initiates transactions)
Protocol 1: Anafaze/AB Communications Protocol
Developed for native integration with Allen-Bradley PLC platforms, the Anafaze/AB protocol defines structured binary packet transmission with standardized control codes, transaction workflows, and dual error-verification mechanisms (BCC/CRC).
Standard Control Code Set
All data packets use escape-based framing with fixed hex control markers:
Standard Packet Frame Structure
Every valid Anafaze/AB packet follows a fixed byte sequence:
Key addressing rule: Controllers use physical address + 7 as the DST destination byte on the communication bus, reserving raw addresses 0–7 for system use.
Error Checking Mechanisms
BCC (Block Check Character)
Single-byte 2’s complement sum verification, lightweight for low-speed networks, suitable for most factory automation deployments. Cannot detect byte transposition or single zero insertion errors.
CRC (Cyclic Redundancy Check)
16-bit high-security validation that catches all single/double bit faults, all odd-bit errors, and 99.998% of burst errors up to 18 bits. Mandatory for high-noise industrial environments.
Transaction Flow Logic
All read/write cycles follow a four-stage handshake with a configurable minimum master delay of 200ms to match controller processing latency. Full error recovery logic includes up to three automatic retransmissions for timeout, NAK, and CRC failure events.
Supported core commands: Block Read (0x01), Block Write (0x08) for bulk parameter access across contiguous data memory blocks.
Anafaze/AB Data Table Architecture
All process variables, PID settings, alarm configurations, and ramp-soak profile data are mapped to fixed hex memory offsets. Data storage rules:
Single-byte types: Unsigned Char (UC), Signed Char (SC)
Dual-byte types: Unsigned Int (UI), Signed Int (SI) (LSB transmitted first)
Channel count constants (MAX_CH) define memory allocation per model:
CLS204: 5 channels; CLS208: 9 channels; CLS216 / MLS316 / CAS200: 17 channels; MLS332: 33 channels
Protocol 2: Modbus® RTU Communications Protocol
Modbus® RTU is the universal industrial standard for third-party PLC, HMI, and SCADA integration, fully implemented across CLS200, MLS300, and CAS200 hardware with complete register mapping for all native controller functions.
Serial Transmission Rules
Silent frame gap: Minimum 3.5 character idle time before/after each message to separate frames
Slave address range: 1–247 (broadcast address 0 for global write commands, no slave response returned)
Mandatory 16-bit CRC error check appended to all messages (LSB transmitted first)
Supported Modbus Function Codes
The controller supports all mainstream read/write commands for discrete and register access:
01 Read Coils (Digital Output Status)
02 Read Discrete Inputs (Digital Input Status)
03 Read Holding Registers (PID, setpoint, profile parameters)
04 Read Input Registers (Process Variables, sensor readings)
05 Force Single Coil
06 Preset Single Register
0F Force Multiple Coils
10 Preset Multiple Registers
08 Diagnostic sub-functions for bus error counting and port reset
Modbus Register Mapping Standard
Two address formats are defined in this specification:
Relative Hex Offset: Raw memory offset for internal engineering reference
Absolute Decimal Address: Industry standard Modbus register notation (40001-series holding registers, 10001-series discrete inputs, 00001-series coils)
All multi-byte values swap byte order automatically between Watlow internal LSB-first storage and Modbus MSB-first transmission. Separate register blocks are allocated for ramp-soak profiles, cascade/ratio advanced control, alarm masking, and digital I/O status.
Global Controller Parameter Library (Chapter 3 Official Reference)
This communications document includes a complete indexed parameter dictionary (1–103) matching front-panel menu items to serial memory addresses, covering all core control features:
Core PID Loop Parameters
Proportional Band (Gain), Integral (TI), Derivative (TD), input type thermocouple/RTD/linear/pulse scaling, process variable (PV), setpoint (SP), heat/cool output percentage, output filter and limit configurations. Each parameter includes fixed value ranges, factory default values, and precision scaling rules (–1 to +4 decimal resolution).
Alarm System Definitions
Full alarm register suite: High/Low Process Alarm, Deviation Alarm, T/C break/reverse detection, ambient calibration warnings. Independent Alarm_Status, Alarm_Mask, Alarm_Enable, Alarm_Control, and Alarm_Acknowledge bitmaps support automatic fault reporting via communications status flags.
Ramp & Soak Profile Functions
Exclusive parameters for profile operation: segment setpoints, hold timers, trigger digital inputs, event digital outputs, tolerance thresholds, and cycle counters. Supports up to 17 independent profiles with 20 configurable segments each.
Advanced Control Options
Cascade control, ratio control, PV retransmission analog output, digital input override, manufacturing test modes, and unit firmware version readback. Separate channel naming logic for CLS/MLS (2-character loop ID) and CAS200 (8-character alarm channel labels).
System Communication Config Parameters
Software-adjustable serial settings accessible via bus: Controller address (1–247), baud rate selector, communication error check mode, digital input job selection, and keyboard lock register. Changes to baud rate and slave address require a full power cycle to activate.
Key Cross-Device Compatibility Notes
Shared Memory Calculation Logic
MAX_CH, MAX_DIGIN, MAX_DIGOUT, MAX_RSP and MAX_SEG constants unify data table sizing across all three product lines, simplifying multi-model software development with a single driver codebase.
CAS200 Exclusive Functions
CAS200 alarm scanner omits heat/cool PID output parameters and expands channel name storage to 8 characters per loop, with dedicated alarm polling registers unique to the scanner module.
MLS300 Multi-Loop Extensions
MLS332 32-loop units extend MAX_CH to 33, with expanded digital I/O register blocks for high-density process monitoring.
Firmware Option Dependencies
Ramp-soak and enhanced cascade/ratio control parameters only populate data tables if the controller is loaded with matching option firmware; unused registers return zero when queried.
