Cocoon POWERTALK 101 - Manual (Page 51)

PowerTALK 101
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PowerTALK 101 protocol
PowerTALK 101 supports the TCP/IP suit of protocols, namely IP, ARP, ICMP and UDP.
Presently it will respond to ICMP Ping and ARP, although it cannot originate Ping requests. ARP
requests are sent. PowerTALK’s own protocol and the transported data are carried inside UDP
datagrams. The data carried is 1 byte minimum (after time out) and128 bytes maximum. The
Ethernet encapsulation is as defined in RFC 894 and mandated by RFC 1022. The packet format
is shown below -
Mac Header -
6 bytes Destination MAC address
6 bytes Source MAC address
2 bytes Type - 0800 for IP packets, 0805 for ARP requests and 0806 for ARP replies.
IP header -
2 bytes IP Version - 4, header length - 20, TOS - 16 (4510h)
2 bytes IP packet length including header
2 bytes identifier (packet number, unique over a short period)
2 bytes fragmentation - 00
2 bytes TTL - 64, protocol - 17 = UDP (4011h)
2 bytes header checksum
4 bytes Source IP number
4 bytes Destination IP number
UDP header -
2 bytes Source port – variable
2 bytes Destination port – 7000dec
2 bytes length of UDP portion including header
2 bytes optional UDP checksum - set to 00
PowerTALK data -
2 bytes command_code // Command code
2 bytes target_comport // Target com port, 1=COM1 etc, -1=broadcast
2 bytes data_length // Length of data in data block
2 bytes source_comport // Source com port of data, 1=COM1 etc
2 bytes sequence // Incrementing sequence nr
2 bytes channel // Channel ID (for broadcasts)
20 bytes reserved // reserved (must be all 0)
128 bytes data // data buffer