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

Key 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

Configuration Parameters

Override Channel Selection

Override State Configuration

Block Inputs

Individual Override Mode

Grouped Override Mode

Block Outputs

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

Usage 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

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

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

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

See Also

• [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