Chapter 6. Serial I/O, SNP & RTU Protocols252 PACSystems* RX7i, RX3i and RSTi-EP CPU Reference Manual GFK-2222AD6.3.4 RTU Scratch PadThe entire scratch pad is updated every time an external READ request is received by the PACSystemsRTU slave. All scratch pad locations are read only. The scratch pad is a byte-oriented memory type.RTU Scratch Pad Memory AllocationSP Address Field Identifier Bits7 6 5 4 3 2 1 000 CPU Run Status 0 0 0 0 See note.8801 CPU Command Status Bit pattern same as SP(00)0203 CPU Type Major89 (in hexadecimal)Minor90 (in hexadecimal)04 – 0B CPU SNP ID 7 ASCII characters + termination character (00h)0C0D CPU Firmware Revision No. Major (in BCD)Minor (in BCD)0E0FCommunications Management Module(CMM) Firmware Revision No.MajorMinor10—11 Reserved 00h12 Node Type Identifier PACSystems 43 (hexadecimal)13—15 Reserved 00h16 RTU Station Address 1—247 (decimal)17 Reserved 00h18—3391 Sizes of Memory Types18—1B Register Memory %R size (words)1C—1F Analog Input Table %AI size (words)20—23 Analog Output Table %AO size (words)24—27 Input Table %I size (bits)28—2B Output Table %O size (bits)2C—2F Internal Discrete Memory %M size (bits)30—33 User Program Code The amount of program memory occupied by the logicprogram.34—FF Reserved 00h88 0000 = Run_Enabled 0100 = Halted 0001 = Run_Disabled0101 = Suspended 0010 = Stopped 0110 = Stopped_IO_Enabled89 CPU Major Type Codes: PACSystems 0x4390 PACSystems Minor Types for CPU: refer to Message (17): Report Device Type91 Four bytes hold the hexadecimal length of each memory type with the most significant word reserved for future expansion.For example, the default register memory size of 1024 words (0400h) would be returned in the following format:Word Least Significant Most SignificantSP Byte 18 19 1A 1BContains 00 04 00 00
