Physical layer and data link interface with adaptive speed

A PHY to transmit and receive signals propagated on a medium, and to communicate with a MAC via PHY-to-MAC words and MAC-to-PHY words, the PHY comprising:

• at least one MAC-to-PHY port to receive signals indicative of the MAC-to-PHY words;
• and
• at least one PHY-to-MAC port to transmit signals indicative of the PHY-to-MAC words;
• wherein the PHY-to-MAC words include slow mode PHY-to-MAC words, wherein a slow mode PHY-to-MAC word transmitted by the PHY and received by the MAC includes a transmit cycle field to indicate whether the MAC is requested by the PHY to provide data for transmission on the medium in a next MAC-to-PHY word transmitted by the MAC to the PHY subsequent to the MAC receiving the slow mode PHY-to-MAC word.

A computer system comprising:

• a MAC;
• and
• a PHY to receive and transmit signals propagated on a medium and connected to the MAC so that the MAC provides MAC-to-PHY words to the PHY and the PHY provides PHY-to-MAC words to the MAC;
• wherein the PHY-to-MAC words and the MAC-to-PHY words are synchronously paired so that the MAC provides one MAC-to-PHY word to the PHY while the PHY provides one PHY-to-MAC word to the MAC;
• wherein the PHY-to-MAC words include slow mode PHY-to-MAC words having a transmit cycle field;
• wherein if the transmit cycle field of a first slow mode PHY-to-MAC word is set to a first value, the first slow mode PHY-to-MAC word being synchronously paired with a first MAC-to-PHY word, then the MAC is requested by the PHY to provide transmit data in a second MAC-to-PHY word for transmission over the medium, where the second MAC-to-PHY word succeeds the first MAC-to-PHY word, and if the transmit cycle field of the first slow mode PHY-to-MAC word is set to a second value different from the first value, then the MAC is requested by the PHY not to include transmit data in the second MAC-to-PHY word.