The Instruction pins, I1-0, control the loading of the registers. For either device, the registers may be configured as a four-stage delay line, with data loaded into R1 and shifted sequentially through R2, R3, and R4. Also, for the L29C520, data may be loaded from the inputs into either R1 or R3 with only R2 or R4 shifting. The L29C521 differs from the L29C520 in that R2 and R4 remain unchanged during this type of data load, as shown in Tables 1 and 2. Finally, I1-0 may be set to prevent any register from changing.