The core supplied for 1 Gbps only operation provides either a GMII or RGMII interface. These are typically used to connect the MAC to an external PHY device. GMII defined in IEEE Std 802.3-2008, clause 35, is used to connect a 1 Gbps capable MAC to the physical sublayers.
For 7 series and Zynq 7000 families, the voltage standard used depends on the type of I/O used: HR I/O supports GMII at 3.3V or lower and HP I/O only supports 1.8V or lower. Therefore an external voltage converter is required to interoperate with any multi-standard PHY for GMII.
RGMII is an alternative to GMII and achieves a 50% reduction in the pin count compared with GMII. Therefore, this is often favored over GMII by Printed Circuit Board (PCB) designers. This configuration is achieved with the use of double-data-rate (DDR) flip-flops.
For 7 series and Zynq 7000 families, the voltage standard used depends on the type of I/O used: HR I/O supports RGMII at 2.5V or lower and HP I/O only supports 1.8V or lower. Despite this being the defined RGMII voltage, most PHYs require 2.5V and therefore an external voltage converter is required to interoperate with any multi-standard PHY for RGMII.