Appendix A – Reducing the amount of data being transferred over the Bus Applicaton Layer You can limit the amount of data being transferred over the Bus, and save both bandwidth and memory, by using P762. However, when you reduce the size of the data map, the configuration will change. If the data block sizes in the device do not match what is configured in the master, no communications will occur. Therefore it is critical to calculate the size of the new map. The calculation is different for level applications and for mass dynamics applications. The following sections provide explanations and examples of the calculation required, together with a worksheet to use as a template.
The first section explains how it works with level products, and the second explains how it works with mass dynamics products. In each section, the Write Block map is calculated first, followed by the Read Block. Level Products The Smartlinx map 1 is controlled by the values of the indices of P762. By turning on an index (setting the value to one or more), you activate both the read and write blocks associated with that index. The table below shows which values in the read/write blocks are turned on by each P762 index. 1. For examples of the data maps before modification, see pages 50 and 52.
Page 48 SmartLinx DeviceNet – INSTRUCTION MANUAL 7ML19981BH02 Name of area P762 Point Value Read area turned On Write area turned on Status 1 1 Instrument status ------------------- Reading 2 1 -10 1-10 point readings ------------------- Alarm 3 1-10 1-10 point alarm and status ------------------- Point on Priority 4 1 ------------------- Measurement point on Priority MPA 5 1 Returned Values (1-10) Parameter number Decimal place Secondary index Format Decimal place Parameter number Format Secondary index -------------------- SPA 6 1 Parameter Number Parameter Number Primary index Primary index Secondary index Secondary index Returned Value New Value Decimal Place Decimal Place Format Format Read/Write Read/ Write Operating Mode 7 1 ----------------------- Operating Mode