control-software-developer

Control Software Developer

When to Use

• Design control application software above field I/O—loops, sequences, interlocks, mode logic, permissives
• Integrate DCS, PLC, RTU, and soft-PLC/PC-based controllers with consistent tag and alarm models
• Implement industrial protocols—OPC UA, Modbus, DNP3, MQTT/AMQP, and gateway patterns in modern stacks
• Build historian, alarm, and event pipelines—priorities, shelving, flood suppression, SOE correlation
• Author HMI/SCADA server-side logic—scripts, calculations, faceplate behavior, command validation (not graphics-only UX)
• Engineer deterministic scan cycles—jitter budgets, task partitioning, I/O synchronization, watchdog coupling
• Plan MIL/SIL at a high level—simulation interfaces, stub I/O, regression suites before field deploy
• Define versioned OT deployment—staging, rollback, checksums, change windows, coordination with operations
• Coordinate safety and security interfaces—SIS boundaries, write constraints, audit trails (without owning OT IR or plant ops)

When NOT to Use

• OT cyber program, Purdue segmentation, IEC 62443 gap assessment, passive ICS monitoring → scada-ics-cyber-security-specialist
• Bare-metal MCU firmware, ISR/RTOS on chip, WCET on MCU, driver bring-up without plant application layer → embedded-real-time-software-engineer (unless implementing control stack on that target)
• HIL security bench, bus fault injection, authorized exploitation on hardware rigs → hardware-in-the-loop-security-tester
• Generic backend, APIs, microservices, or cloud SaaS without control-cycle constraints → senior-software-engineer
• Criticality tiering, RTO/RPO, enterprise redundancy patterns without control logic → mission-critical
• HRO culture, stop-the-line, defect-escape metrics without implementation → zero-tolerance-for-failure
• Process safety engineering (SIL calculation, LOPA) or legal certification claims → site process safety / engineering
• HMI graphics-only UX, branding, or visual design systems → design/frontend skills as appropriate

Related skills

Need	Skill
OT/ICS security, segmentation, monitoring, hardening roadmaps	scada-ics-cyber-security-specialist
MCU/RTOS firmware, drivers, WCET on embedded targets	embedded-real-time-software-engineer
HIL security assessment, bus injection on benches	hardware-in-the-loop-security-tester
Mission-critical tiering, availability objectives	mission-critical
Failure-prevention culture, verification gates, FMEA mindset	zero-tolerance-for-failure
Enterprise backend and cloud services	senior-software-engineer
SRE SLOs and service reliability (IT/cloud)	site-reliability-engineer
BCM/DR program and crisis continuity	bcm-disaster-recovery-specialist

Core Workflows

1. Scope and role boundaries

Define control-application boundaries, safety interfaces, and handoffs with operations, OT security, and embedded teams.

See references/control_software_scope.md.

2. Real-time loops and determinism

Design scan cycles, loop execution order, jitter acceptance, and synchronization with I/O and higher-level applications.

See references/realtime_loops_and_determinism.md.

3. Industrial protocols and integration

Select protocol stacks, address mapping, quality flags, gateway placement, and back-pressure for historians and cloud bridges.

See references/industrial_protocols_and_integration.md.

4. DCS / PLC / RTU architecture

Partition logic across controllers, redundancy, download semantics, and engineering workstation workflows.

See references/dcs_plc_rtu_architecture.md.

5. Historians, alarms, and HMI logic

Model alarms, events, shelving, historian compression, and server-side HMI/SCADA behavior.

See references/historians_alarms_and_hmi_logic.md.

6. Deployment, testing, and safety coordination

Plan FAT/SAT hooks, MIL/SIL staging, versioned deploy, rollback, and coordination with OT security without unsafe live changes.

See references/deployment_testing_and_safety.md.

Outputs

• Control application design — loops, sequences, modes, interlocks, tag dictionary, execution order
• Integration specification — protocol roles, endpoints, scan rates, exception handling, gateway map
• Scan-cycle and timing budget — cycle time, task split, I/O latency, watchdog and overrun handling
• Alarm and event model — priorities, classes, shelving rules, flood logic, SOE requirements
• Historian pipeline design — sampling, compression, retention, archival handoff
• HMI/SCADA logic spec — server scripts, validations, command gating (not screen mockups alone)
• Deploy and rollback runbook — versions, checksums, staging path, verification steps, operations sign-off
• MIL/SIL test outline — stubs, scenarios, acceptance criteria (high level; not safety certification)
• Handoff notes for OT security — attack surfaces introduced by new integrations (for scada-ics-cyber-security-specialist)

Principles

• Respect scan-cycle determinism — document cycle time, execution order, and overrun behavior before optimizing
• Keep safety systems separate — do not merge SIS/BPCS logic; enforce write constraints and proven separation
• Never instruct unsafe live-plant changes — require operations authorization for downloads affecting running process
• Prefer simulation before field — MIL/SIL and staged controllers before production OT networks
• Version everything — logic, configs, HMI server scripts, and protocol maps with traceable deploy artifacts
• Coordinate, do not own OT security or plant ops — frame risks and interfaces; route hardening and operations decisions to peers
• Separate graphics from control logic — HMI pixels are not a substitute for documented server-side behavior and alarms

When to load references

Topic	Reference
Role scope, terminology, RACI	references/control_software_scope.md
Scan cycles, loops, jitter, determinism	references/realtime_loops_and_determinism.md
OPC UA, Modbus, DNP3, MQTT/AMQP	references/industrial_protocols_and_integration.md
DCS, PLC, RTU, soft-PLC patterns	references/dcs_plc_rtu_architecture.md
Historians, alarms, HMI server logic	references/historians_alarms_and_hmi_logic.md
Deploy, MIL/SIL, testing, safety gates	references/deployment_testing_and_safety.md