MFi PTT Protocol Specification

Version: 1.1
EA Protocol Name: com.pttsdk.ea.protocol
Date: May 15, 2026

A custom MFi protocol for certified accessories (e.g., headsets, speaker‑mics, control panels) to interact with iOS apps for Push‑to‑Talk with low latency and secure, reliable behavior across devices.

Introduction

A Custom MFi Protocol is a proprietary communication standard developed under Apple's Made for iPhone/iPad (MFi) program. It enables certified accessories to interact with iOS devices using specialized commands beyond standard USB or Bluetooth profiles.

Benefits

• Optimized Performance: Real‑time control of PTT functions like press/release, channel switching, and emergency signaling with minimal latency.
• Secure Communication: Uses Apple's authentication and optional encryption to ensure trusted accessory‑device interaction.
• Extended Functionality: Supports advanced features like AI assistant activation and device status reporting.
• User Experience Consistency: Reliable behavior across certified accessories, improving usability in mission‑critical environments.
• Integration Flexibility: Tailorable to public safety, logistics, or enterprise communication workflows.

PTT commands

Call control commands

Other commands

Packet Structures

Request / Notify Packet Structure

        
byte 1: 0x3C                        // Start 
byte 2: 0x00 or 0x02                // Command type (0x00 = Request, 0x02 = Notify)
byte 3-4: Command (UInt16)          // Command ID (big-endian)
byte 5-6: Data length (UInt16)      // Payload length (big-endian)
byte 7..(7+N): Data (optional)      // Payload bytes
byte 8+N: 0x3E                      // End byte
            
        

Response Packet Structure

        
byte 1: 0x3C                        // Start byte
byte 2: 0x01                        // Response type
byte 3-4: Command (UInt16)          // Original command ID (big-endian)
byte 5-6: Response code (UInt16)    // Response code (big-endian)
byte 7: 0x3E                        // End byte
            
        

Payload Examples

3C 02 10 01 00 00 3E

3C 02 10 02 00 00 3E

3C 02 10 03 00 00 3E

3C 02 10 04 00 00 3E

3C 02 10 05 00 00 3E

3C 02 10 0A 00 00 3E

3C 02 10 0B 00 00 3E

3C 02 20 00 00 00 3E

3C 02 20 01 00 00 3E

3C 02 20 02 00 00 3E

3C 02 30 00 00 00 3E

3C 02 30 01 00 00 3E

3C 02 40 00 00 00 3E

3C 02 40 01 00 00 3E

3C 02 50 00 00 00 3E

3C 02 50 01 00 00 3E

3C 02 50 02 00 00 3E

3C 02 50 03 00 00 3E

3C 00 60 00 00 00 3E

3C 02 60 00 00 01 08 3E

3C 00 60 01 00 01 08 3E

3C 02 99 99 00 00 3E

iOS Reference Code Sample

Info.plist Changes

    <key>UISupportedExternalAccessoryProtocols</key>
    <array>
    <string>com.pttsdk.ea.protocol</string>
    </array>

Swift — Connect and Parse Changes

    import Foundation
    import ExternalAccessory

    class MFiAccessoryManager: NSObject, StreamDelegate {
    private var session: EASession?
    private var inputStream: InputStream?
    private var outputStream: OutputStream?
    private let protocolString = "com.pttsdk.ea.protocol"

    func connect() {
    let accessories = EAAccessoryManager.shared().connectedAccessories
    guard let accessory = accessories.first(where: { $0.protocolStrings.contains(protocolString) }) else {
    print("No accessory found for protocol \(protocolString)")
    return
    }

    session = EASession(accessory: accessory, forProtocol: protocolString)
    inputStream = session?.inputStream
    outputStream = session?.outputStream

    [inputStream, outputStream].forEach { stream in
    stream?.delegate = self
    stream?.schedule(in: .current, forMode: .default)
    stream?.open()
    }
    }

    // MARK: - StreamDelegate
    func stream(_ aStream: Stream, handle eventCode: Stream.Event) {
    switch eventCode {
    case .hasBytesAvailable:
    parseIncomingData()
    case .errorOccurred:
    print("Stream error: \(String(describing: aStream.streamError))")
    case .endEncountered:
    print("Stream ended")
    default:
    break
    }
    }

    private func parseIncomingData() {
    guard let inputStream = inputStream else { return }
    var buffer = [UInt8](repeating: 0, count: 1024)
    let bytesRead = inputStream.read(&buffer, maxLength: buffer.count)
    guard bytesRead > 0 else { return }

    let data = Array(buffer.prefix(bytesRead))
    var index = 0

    while index < data.count {
    guard data[index] == 0x3C else {
    index += 1
    continue
    }

    guard index + 6 < data.count else { break }

    let commandType = data[index + 1]
    let commandID = UInt16(data[index + 2]) << 8 | UInt16(data[index + 3])
    let dataLength = UInt16(data[index + 4]) << 8 | UInt16(data[index + 5])

    let payloadStart = index + 6
    let payloadEnd = payloadStart + Int(dataLength)

    guard payloadEnd < data.count, data[payloadEnd] == 0x3E else {
    print("Invalid or incomplete message")
    break
    }

    let payload = Array(data[payloadStart..<payloadEnd])
    handleCommand(commandType: commandType, commandID: commandID, payload: payload)
    index = payloadEnd + 1
    }
    }

    private func handleCommand(commandType: UInt8, commandID: UInt16, payload: [UInt8]) {
    let hexID = String(format: "0x%04X", commandID)
    print("Received Type: \(commandType), ID: \(hexID), Payload: \(payload)")

    switch commandID {
    case 0x1001: print("PTT_PRESS")
    case 0x1002: print("PTT_LONG_PRESS")
    case 0x1003: print("PTT_DOUBLE_PRESS")
    case 0x1004: print("PTT_TRIPLE_PRESS")
    case 0x1005: print("PTT_RELEASE")
    case 0x100A: print("CHANNEL_UP")
    case 0x100B: print("CHANNEL_DOWN")
    case 0x2000: print("ACCEPT_CALL")
    case 0x2001: print("END_CALL")
    case 0x2002: print("HOLD_CALL")
    case 0x3000: print("MUTE")
    case 0x3001: print("UNMUTE")
    case 0x4000: print("AI_ASSISTANT")
    case 0x4001: print("REPLAY")
    case 0x5000: print("STATUS_TOGGLE")
    case 0x5001: print("STATUS_AVAILABLE")
    case 0x5002: print("STATUS_BUSY")
    case 0x5003: print("STATUS_SOLO")
    case 0x9999: print("EMERGENCY_TRIGGER")
    default:     print("Unknown command: \(hexID)")
    }
    }
    }

Revisions