PWM HighSpeed Override

dsPIC33F dsPIC33E GS dsPIC33C CK/CH

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The override block works in conjunction with the MCHP_PWM_HighSpeed block and can force PWM outputs to specific logic levels regardless of the PWM generator state. Important: Override control should be used with extreme caution in motor control applications, as improper use can cause hardware damage or create hazardous conditions. ## Supported Device Families This block supports the same device families as MCHP_PWM_HighSpeed: - dsPIC33F (selected) - with high-speed PWM module - dsPIC33EP (GS) - with auxiliary clock support - dsPIC33C/CH/CK - full-featured implementations

When to use:

• Emergency shutdown and manual override control for PWM HighSpeed block outputs
• Diagnostic mode for individual phase/gate testing
• Custom commutation patterns for BLDC motors
• Shoot-through protection when software override is required

When NOT to use:

• Primary PWM generation → use PWM HighSpeed block
• Override on SAM7x devices → use PWM SAM7x Override
• Devices without high-speed PWM peripheral → use standard PWM with built-in OVDCON control

Parameters

Override Channel Selection

Override State Configuration

Block Inputs

Individual Override Mode

Grouped Override Mode

Block Outputs

Safety Considerations

⚠️ Critical Safety Guidelines

• Never enable both high and low side simultaneously unless using push-pull mode with appropriate hardware
• Always configure safe default states before enabling override
• Test override logic thoroughly on bench before motor connection
• Implement timeout protection to revert to safe state if control loop fails
• Use hardware fault inputs as primary protection; override is secondary

Recommended Safe States

Features

• Direct control of PWM output pins (PWMxH and PWMxL)
• Individual or grouped override control
• Override enable/disable per channel
• Synchronization with PWM generator (optional)
• Support for safe state configuration
• Runtime override value modification

Examples

Example 1: Emergency Shutdown

% Configuration:
% OverrideChannels = [1 2 3];  % All motor phases
% OverrideMode = 'Grouped';
% DefaultState_H = 0;           % All high-sides OFF
% DefaultState_L = 0;           % All low-sides OFF
% SyncMode = 'Immediate';       % Fastest response

% Model logic:
% Connect emergency stop button -> Override_En input
% When E-stop pressed: all outputs forced LOW immediately

% Simulink implementation:
%  [E_Stop] ──→ [Override_En]
%  [0]      ──→ [Override_Value]  % All bits 0 = all outputs LOW

Example 2: Diagnostic Mode - Individual Phase Test

% Configuration:
% OverrideChannels = [1 2 3];
% OverrideMode = 'Individual';

% Test sequence (executed by state machine):
% 1. Override PWM1: High-side ON, Low-side OFF
% 2. Measure current
% 3. Override PWM1: High-side OFF, Low-side ON
% 4. Measure current
% 5. Repeat for PWM2, PWM3

% Block inputs:
%  Override_En_1 = test_active && (phase == 1);
%  Override_H_1 = test_state == HIGH_SIDE_TEST;
%  Override_L_1 = test_state == LOW_SIDE_TEST;

Example 3: Custom Commutation Pattern (BLDC)

% For 6-step BLDC commutation with hall sensors:
% OverrideChannels = [1 2 3];
% OverrideMode = 'Grouped';

% Commutation table (hall sensor state -> override value):
% Hall = 001: PWM1H=1, PWM1L=0, PWM2H=0, PWM2L=1, PWM3H/L=0
% Hall = 010: ...

commutationTable = [
    bin2dec('000000'),  % Hall 000 (invalid)
    bin2dec('100001'),  % Hall 001
    bin2dec('001100'),  % Hall 010
    bin2dec('101100'),  % Hall 011
    bin2dec('110010'),  % Hall 100
    bin2dec('110001'),  % Hall 101
    bin2dec('011010'),  % Hall 110
    bin2dec('000000')   % Hall 111 (invalid)
];

% Model:
%  [Hall_State] ──→ [Lookup Table] ──→ [Override_Value]
%                   (commutationTable)
%  [BLDC_Mode]  ──→ [Override_En]  % Enable override in BLDC mode

Example 4: Shoot-Through Protection

% Prevent both high and low side ON simultaneously:
% OverrideChannels = [1 2 3];
% OverrideMode = 'Individual';
% SyncMode = 'Synchronized';  % Avoid glitches

% Protection logic (for each channel):
%  if (PWM_H_command && PWM_L_command)  % Illegal state
%      Override_En = 1;
%      Override_H = 0;
%      Override_L = 0;
%  else
%      Override_En = 0;  % Normal PWM operation
%  end

Troubleshooting

Override Not Working

Possible Causes:

• Fault input active (fault has higher priority than override)
• Incorrect channel numbering (check enabled channels in PWM_HighSpeed block)
• Override disabled in IOCONx register (check TLC code generation)

Unexpected Output States

Solutions:

• Verify Override_Value bitfield mapping matches hardware PWM numbering
• Check for conflicts with PWM output polarity settings (PENH/PENL in IOCONx)
• Ensure synchronized mode is used if immediate override causes glitches

Shoot-Through During Override Transition

Symptom: Momentary short circuit during override enable/disable Solutions:

• Use synchronized mode (SyncMode = ‘Synchronized’)
• Implement software dead-time in override logic
• Sequence override transitions: first disable old state, wait dead-time, then enable new state

Implementation Details

Hardware Registers

The override block configures the following registers:

Override Priority

When multiple control mechanisms are active, the priority order is:

• Fault override (highest priority) - hardware fault forces outputs to safe state
• Manual override (this block) - software controlled override
• Normal PWM (lowest priority) - PWM generator output

Related Blocks

• MCHP_PWM_HighSpeed - Main PWM block (required for override block to function)

• MCHP_PWM - Standard PWM (has built-in OVDCON register control)

• MCHP_PWM_SAM7x_Override - Override block for SAM7x devices

• MCHP_Comparator - Hardware fault generation

• [Peripheral Block Overview](../

• Safety and Fault Handling Guide

• dsPIC33F/EP Family Reference Manual - PWM Override Control

• dsPIC33C Family Reference Manual - Output Override and Polarity Control