Token bus communication system
In a token bus system a node with the token can transmit on the bus a packet that contains two destination addresses. One address specifies the node that should receive the data component (payload) of the transmitted packet. The other address specifies the node that should receive the token. The network protocol specifies that a node with the token must immediately transmit a packet containing just the token or a packet with token and data if it has data to send. When no data is being passed from one node to another on the network, the token may be passed from one node to the next in order. Each node will pass the token to the next highest node number. If a node has the token has some data for sending it transmits a packet with the token for the next node and data for any of the nodes. The bus system requires every node to receive all packets and process them to determine whether the token or the data (or both) is destined for that node.
1. A token bus communication system comprising a multiplicity of nodes connected by a common bus, wherein each of the multiplicity of nodes is organized:
(i) when in possession of a token and having data to transmit, to transmit a ‘token and data’ packet including a payload and having a header including a first address field identifying which node is to receive the token and a second address field identifying which node is to receive the payload;
(ii) when in possession of a token and having no data to transmit, to transmit a ‘token only’ packet having said first and second address fields, wherein said first address field identifies which node is to receive the token and said second address field identifies none of said nodes; and
(iii) to receive from other nodes ‘token & data’ and ‘token only’ packets and to determine whether a token and/or data is destined for that node;
and wherein:
(a) each of the nodes in the multiplicity thereof is operative to have a master state in which it determines the identity of all of the other nodes in operative connection with the common bus and broadcasts to all the other nodes a sequence table which specifies an order for the reception of the token; and
(b) each of the nodes in the multiplicity thereof is operative to have at least one run state in which, in response to reception of the token, it transmits the token immediately to the node next following it in the sequence table.
2. The token bus communication system of claim 1 , wherein each of the nodes in the multiplicity thereof is organized on entry into a master state to perform a search to determine the identities of all the other nodes in operative connection with the bus.
3. The token bus communication system of claim 2 , wherein said search is a recursive search wherein ever-reducing ranges of addresses are searched until for each range not more than one node is detected.
4. The token bus communication system of claim 3 , wherein each of the nodes in the multiplicity thereof is operative in a master state to determine from silence on the bus for more than a predetermined time that a node failed to respond to the transmission of the token and thereupon to send a ‘token only’ packet to the node next in the sequence table after he node that failed to respond.
5. A token bus communication system comprising a multiplicity of nodes connected by a common bus, wherein each of the multiplicity of nodes is organized:)
(i) when in possession of a token and having data to transmit, to transmit a ‘token & data’ packet including a payload and having a header including a first address field for identifying which node is to receive the token and a second address field for identifying which node is to receive the payload;
(ii) when in possession of a token and having no data to transmit, to transmit a ‘token only’ packet having said first and second address fields, wherein said first address field identifies which node is to receive the token and said second address field identifies none of the said nodes; and
(iii) to receive from other nodes ‘token & data’ and ‘token only’ packets and to determine whether a token and/or data is destined for that node;
wherein all said packets have a common frame structure including a command field which has a first value for a ‘token & data’ packet and a second value for a ‘token only’ packet;
and wherein:
(a) each of the nodes in the multiplicity thereof is operative to have a master state in which it determines the identity of all of the other nodes in operative connection with the common bus and broadcasts to all the other nodes a sequence table which specifies an order for the reception of the token; and
(b) each of the nodes in the multiplicity thereof is operative to have at least one run state in which, in response to reception of the token, it transmits the token immediately to the node next following it in the sequence table.
6. The token bus communication system of claim 5 , wherein each of the nodes in the multiplicity thereof is organized on entry into its master state to perform a search to determine the identities of all the other nodes in operative connection with the bus.
7. The token bus communication system of claim 6 , wherein said search is a recursive search wherein ever-reducing ranges of addresses are searched until for each range not more than one node is detected.
8. The token bus communication system of claim 7 , wherein each of the nodes in the multiplicity thereof is operative in a master state to determine from silence on the bus for more than a predetermined time that a node has failed to respond to the transmission of the token and thereupon to send a ‘token only’ packet to the node next in the sequence table after the node that failed to respond.
9. A token bus communication system comprising a multiplicity of nodes connected by a common bus, wherein each of the multiplicity of nodes is organized:
(i) when in possession of a token and having data to transmit, to transmit a ‘token & data’ packet including a payload and having a header including a first destination address field for identifying which node is to receive the token, a second destination address field for identifying which node is to receive the token and a command field identifying this packet as a ‘token & data’ packet;
(ii) when in possession of a token and having no data to transmit, to transmit a ‘token only’ packet having a header including a destination address field identifying which node is to receive the token and a command field identifying this packet as a ‘token only’ packet; and
(iii) to receive from other nodes ‘token & data’ and ‘token only’ packets and to determine whether a token and/or data is destined for that node;
and wherein:
(a) each of the nodes in the multiplicity thereof is operative to have a master state in which it determines the identity of all of the other nodes in operative connection with the common bus and broadcasts to all said other nodes a sequence table which specifies an order for the reception of the token; and
(b) each of the nodes in the multiplicity thereof is operative to have at least one run state in which, in response to reception of the token, it transmits the token immediately to the node next following it in the sequence table.
10. The token bus communication system of claim 9 , wherein each of the nodes in the multiplicity thereof is organized on entry into its master state to perform a search to determine the identities of all the other nodes in operative connection with the bus.
11. The token bus communication system of claim 10 , wherein said search is a recursive search wherein ever-reducing ranges of addresses are searched until for each range not more than one node is detected.
12. The token bus communication system of claim 9 , wherein each of the nodes in the multiplicity thereof is operative in a master state to determine from silence on the bus for more than a predetermined time that a node has failed to respond to the transmission of the token and thereupon to send a ‘token only’ packet to the node next in the sequence table after the node that failed to respond.