The amount of data moved by the single-operand transfer of the DMAC differs depending on the transfer data size select bits (SZSEL) and the operand transfer data count select bits (OPSEL) in the DMA mode register (DMMOD). The SZSEL bits select the bit length of each transfer and the OPSEL bits select how many transfers occur.
Consequently, when the SZSEL bits select 8 bits per transfer the maximum number of bytes that can be transferred by a single-operand transfer is 128 bytes because the maximum number of transfers that can be selected using the OPSEL bits is 128. When the SZSEL bits select 16 bits per transfer 256 bytes can be transferred, and when it is 32 bits 512 bytes can be transferred.
For details, please refer to DMA Mode Register (DMMOD) in the DMA Controller (DMAC) chapter of the hardware manual.