Series 2000 Communications Handbook - Soliton

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MODBUS and JBUS ProtocolSeries 2000 Communications Handbook3.2. TYPICAL TRANSMISSION LINE ACTIVITYThis diagram is to illustrate typical sequence of events on a Modbus transmission line.ACTIVITYMasterTo slave 1bTo slave NbBroadcastcSlave 1aReplyaSlave NaReplyaNetworkMasterSlave 1MasterSlave 2MasterTIME >Period 'a' The processing time, (latency), required by the slave to complete the command andconstruct a reply.Period 'b' The processing time required by the master to analyse the slave response andformulate the next command.Period 'c' The wait time calculated by the master for the slaves to perform the operation.None of the slaves will reply to a broadcast message.For a definition of the time periods required by the network, refer to 'Wait Period' in thesection 'Error Response'.3.3. DEVICE ADDRESSEach slave has a unique 8 bit device address. The Gould MODBUS Protocol defines theaddress range limits as 1 to 247. Series 2000 instruments will support an address range of 1to 254. The device address used by the instrument is set using the 5 parameter in the, )O6, which is available in operator mode. Note that this list may only be accessiblewhen using the 9)) user interface: refer to the manual supplied with the instrument formore details on how to set this parameter.Device address 0 is a special case that will broadcast a message to all slave devicessimultaneously.3-4 Series 2000 Communications Handbook Part No HA026230 Issue 2.0 Feb-00
Series 2000 Communications HandbookMODBUS and JBUS Protocol3.4. PARAMETER ADDRESSData bits or data words exchange information between master and slave devices. This dataconsists of parameters. All parameters communicated between master and slaves have a 16bit parameter address.The MODBUS parameter address range is 0001 to FFFF..Parameter definitions for Series 2000 instruments are in Chapter 5.3.5. PARAMETER RESOLUTIONJBUS and MODBUS protocol limit data to 16 bits per parameter. This reduces the activerange of parameters to 65536 counts. In Series 2000 instruments this is implemented as -32767 (8001h) to +32767 (7FFFh).The protocol is also limited to integer communication only. Series 2000 instruments allowthe user to configure either integer or full resolution. In integer mode all parameters will berounded to the nearest integer value, whereas in full resolution mode the decimal pointposition will be implied so that 100.01 would be transmitted as 10001. From this, and the 16bit resolution limitation, the maximum value communicable with 2 decimal place resolutionis 327.67. The parameter resolution will be taken from the slave user interface, and theconversion factor must be known to both master and slave when the network is initiated.The Series 2000 instruments provide a special sub-protocol for accessing full resolutionfloating point data. This is described in Chapter 6 of this manual.3.6. MODE OF TRANSMISSIONThe mode of transmission describes the structure of information within a message and thenumber coding system used to exchange a single character of data.The JBUS and MODBUS Protocols define a mode of transmission for both ASCII and RTUmodes of transmission. Series 2000 instruments only support the RTU mode oftransmission.The RTU definition of the mode of transmission for a single character is;A start bit, eight data bits, a parity bit and one or two stop bitsAll Series 2000 instruments use 1 stop bit.Parity may be configured to be NONE, ODD or EVEN.If parity is configured to be NONE, no parity bit is transmitted.The RTU mode of transmission for a single character is represented as follows:Start d7 d6 d5 d4 d3 d2 d1 d0 Parity StopSeries 2000 Communications Handbook Part No HA026230 Issue 2.0 Feb-00 3-5
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Series 2000 Communications Handbook - Soliton

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