LD - Load Data from Data Space Using Indirect Addressing

The LD instruction is used to load data from the data space and into the PHY layer shift register for serial readout. The LD instruction is based on indirect addressing, which means that the Address Pointer in the UPDI needs to be written before the data space read access. Automatic pointer post-increment operation is supported and is useful when the LD instruction is utilized with the REPEAT instruction. It is also possible to do an LD from the UPDI Pointer register. The maximum supported size for address and data load is 32 bits.

Figure 1. LD Instruction Operation

Figure 1 shows an example of a typical LD sequence, where the data are received after the Guard Time (GT) period. Loading data from the UPDI Pointer register follows the same transmission protocol.

For the LD instruction from the data space, the pointer register must be set up by using an ST instruction to the UPDI Pointer register. After the ACK has been received on a successful Pointer register write, the LD instruction must be set up with the desired DATA SIZE operands. An LD to the UPDI Pointer register is done directly with the LD instruction.