KT148A Voice Chip Issue: Difficult to Play with Code Sending - Normal Playback After Grounding Pin 4, What’s the Reason?

Problem Description:

Hello, we’ve encountered an issue and would appreciate your support:
With the KT148A chip, after powering on, sending the code rarely triggers playback. However, if we use tweezers to briefly short Pin 4 (PB0) to ground and then send the code again, playback works normally. What could be causing this?

Based on the observed behavior, it’s highly likely an issue with the timing of one-wire communication, particularly with the start signal, which may be too short. Let’s analyze this in detail and review the KT148A schematic as follows:

1.Pin 4 (PB0) of the Chip: PB0 is a test pin with the default factory function of triggering wake-up and playback when grounded.

2.Customer Description: When the customer uses tweezers to short PB0 (Pin 4) to ground, it follows this principle. The shorting action actually performs two operations:

Action 1: The KT148A detects a falling edge signal, wakes up, exits low-power mode, and enters full-speed operation.

Action 2: The KT148A receives a key press signal and starts playing audio.

3.Hypothesis: The required start signal length differs between the chip's full-speed operation and sleep state. In sleep mode, the chip requires “wake-up time + one-wire start time,” whereas in full-speed operation, only the “start time” is needed.

4.Observation: After triggering Pin 4 with tweezers to wake the chip, sending one-wire data to the KT148A results in normal playback. This indicates that the start signal is likely too short.
Conclusion: The issue is likely due to a start signal that is too short, causing the KT148A to fail to recognize commands after waking up. For detailed guidance, refer to the document “Precautions for KT148A One-Wire Communication and Common Debugging Issues_V2.pdf.”

 Recommended Start Signal Length: 6ms.
The user manual also describes the start signal in Section 3.4:

 
The low-level duration of the start signal is standardized to be between 5.5ms and 6.5ms, with 6ms recommended. An error margin of ±10% is acceptable.

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Refined AI Summary:
Based on the issue description, the KT148A voice chip struggles to trigger playback after power-on when sending codes, but playback works normally after briefly shorting Pin 4 (PB0) to ground with tweezers. This suggests the problem lies in the one-wire communication start signal length. In sleep mode, the chip requires both “wake-up time + start signal time,” while in full-speed mode, only the “start signal time” is needed. Shorting PB0 performs two actions: waking the chip from low-power mode and triggering playback. A start signal that is too short likely prevents the chip from recognizing commands post-wake-up. According to the documentation, the start signal’s low-level duration should be between 5.5ms and 6.5ms, with 6ms recommended and a ±10% error margin. To resolve the issue, verify and adjust the start signal length to ensure proper command recognition and execution by the KT148A.