5.4.5 Y Address Generation Unit

The Y data memory space has one AGU that supports data reads from the Y data memory space. The Y memory bus is never used for data writes. The function of the Y AGU and Y memory bus is to support concurrent data reads for DSP class instructions.

The Y AGU can generate an EA within the data space address range 0x0000 to 0xFFFFFF.

The Y AGU timing is identical to that of the X RAGU, in that its EA calculation starts prior to the instruction cycle, using information derived from the pre-fetched instruction. The EA is presented to the address bus at the beginning of the instruction cycle.

The Y AGU supports Modulo Addressing and Post-Modification Addressing modes for the DSP class of instructions that use it.

Note: The Y AGU does not support data writes. All data writes occur via the X WAGU to the combined X and Y data spaces. The Y AGU is only used during data reads for dual source operand DSP instructions.