Abstract: A data transmission apparatus includes: a first port and a second port which are selected by a first control signal; a first signal path and a second signal path which are selected by a second control signal. When a memory card satisfies a first condition, the first control signal selects the first port and the second control signal selects the first signal path, the data transmission apparatus connects the host device and the memory card via the first port and the first signal path and works in a first transmission mode. When the memory card satisfies a second condition, the first control signal selects the second port and the second control signal selects the second signal path, the data transmission apparatus connects the host device and the memory card via the second port and the second signal path and works in a second transmission mode.