Telemetry protocol for ultra low error rates useable in implantable medical devices

An improved telemetry protocol for an implantable medical device is disclosed. The sending device forms a block of information to be telemetered to the receiving device in a typical fashion, including a header, a message, and an error detection data, such as a Cyclic Redundancy Code (CRC) for that data. This CRC, called CRC1, is preferably computed using a first CRC polynomial. Then, the entirety of the block is divided into smaller packets of a predetermined byte size. Each packet, regardless of its contents, has a CRC computed for it (CRC2) preferably computed using a second CRC polynomial. Each packet with its appended CRC2 is sent to the receiving device, which deduces a CRC2 and compares it with the appended CRC2. If not valid, that packet is again requested to be resent. If valid, the next packet is requested to be sent, its CRC2 checked, etc., until all packets are received and verified. The receiving device then discards the CRC2s to reconstitute the original block. The receiving device then deduces CRC1 and compares it with the CRC1 appended to the block. If valid, the block is accepted, and if not, the procedure is repeated for the block.