Analog Devices ADSP-BF53x Blackfin Reference page 380

Instruction Overview
Also See
None
Special Applications
To write consecutive, 8-bit values for high-performance DSP operations,
use the Store Data Register instructions instead of these byte instructions.
The byte store instructions use only one fourth the available 32-bit data
bus bandwidth, possibly imposing a bottleneck constriction in the data
flow rate.
8-56 ADSP-BF53x/BF56x Blackfin Processor Programming Reference