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I need to transmit a block of 24-bit words via interrupt-driven SCI of 563xx. User manual says that I can efficiently unpack and transfer the 3-bytes comprising the word to the SCI Transmit Register (STX) by writing to STXL, STXM, and STXH. What I'd like to do in my ISR is to do three successive writes of a 24-bit word to STXL, STXM, and STXH, then increment my pointer and exit, and the SCI would send out 3 bytes. This would be efficient. But if I understand the manual correctly, I must first wait for the byte I wrote to STXL to be transmitted, then write to STXM, wait, and then write to STXH. So my question is, how is that more efficient? Am I missing something? Anyone out there use this SCI feature?

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