QPC6614 – Serial control via SPI (6-bit word vs 8-bit SPI frame)

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1

Hi,

I’m using the QPC6614 in serial control mode.
Connections:
• MCU SPI MOSI → SERIN
• MCU SPI SCK → CLK
• LE is driven by a GPIO (high after the last clock, as in the timing diagram).

According to the datasheet the device expects a 6-bit control word (D5…D0), but my MCU hardware SPI always transmits 8-bit frames.

I’d like to clarify how the QPC6614 behaves when more than 6 clock pulses are applied:
1. If I send 8 bits on SERIN with 8 CLK pulses and then toggle LE, which 6 bits are actually latched?
• The first 6 bits shifted in?
• The last 6 bits shifted in?
• Or does the internal shift register “roll over” in some way?
2. Is it acceptable to always send 8 bits and rely on the device to ignore the extra bits, or must I guarantee exactly 6 clock edges between LE transitions?

Thanks in advance for clarifying how to correctly interface the QPC6614 to a standard 8-bit SPI peripheral.

Kind Regards,
Milan

2

The bits latched are the last 6 bits presented on SERIN before LE goes high. If you send 8 SPI clocks per frame, the QPC6614 will clock in 8 bits, but only the last 6 bits before LE is asserted will be latched. Any extra bits (the first 2, if sending 8 bits) will be shifted out and ignored.

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