The Microchip HCS301 was once the most widely used system on garage and gate remote control and receivers. The chip uses the KeeLoq algorithm. The HCS301 KeeLoq system transmits 66 data bits. Thirty-four34 bits are not encrypted: a 28-bit serial number, 4 bits of button information, and 2 status bits (repeat and low battery indicators). Thirty-two32 bits (the rolling code) are encrypted: 4 bits of button information, 2 bits of OVR (used to extend counter value), 10 bits of DISC (discrimination value; often the low ten10 bits of the serial number), and a 16-bit counter.<ref>{{Citation |last=Microchip |title=HC301 KeeLoq Code Hopping Encoder |year=2001 |id=DS21143B |publisher=Microchip Technology Inc. |___location= |url=http://ww1.microchip.com/downloads/en/devicedoc/21143b.pdf}}</ref> In a resyncing situation, the encrypted 32 bits are replaced with a 32-bit seed value.
