Alfa Instrumentos 3000C / 3000C.S Modbus register map

Sources and notes

• Comandos para Indicadores de Pesagem no Protocolo Modbus-RTU - Linha 3000C / 3000C.S · version 4.3, 2009-08-13
  Section 6.3, commands available in the indicators

Source: Alfa Instrumentos, Comandos para Indicadores de Pesagem no Protocolo Modbus-RTU, Linha 3000C / 3000C.S, revision 4.3

• Registers are numbered as in the manual, which counts from 1 (address_base 1): register 81 is sent on the wire as address 80. The manual's own examples show this (reading 6 registers from register 81 sends 0 80).
• Supported functions: 0x03 read, 0x06 write one register, 0x10 write several registers.
• Each block must be read or written whole: a request that covers only part of a block fails with an exception. The blocks are: 21; write 31 to 39 (9 registers); read 41 to 49 (9); write 51 to 56 (6); read 61 to 66 (6); 71; read 81 to 86 (6); 91; write 101 to 105 (5); read 111 to 115 (5); read 141 to 147 (7); write 161 to 166 (6); read 171 to 177 (7); read 181 and 182 (2); 231; 251; 271; write 851 and 852 (2); read 811 to 819 (9).
• The level (SetPoint) and clock blocks are written at one address and read at another, so the write registers are marked W and the read registers R. The level write block holds the levels of one bank (HI: levels 4 to 7, LO: levels 0 to 3) chosen in register 31, and all four values must be sent together.
• Weight, tare and the other 32-bit values are a high register followed by a low one: (register n x 65536) + register n+1, which is the default big word order. The manual gives the sign of the weight as a flag (bit 3 of register 81) and does not state a signed type, so they are read as unsigned. Divide by 10 to the power of the decimal places in bits 0 to 2 of register 81.
• The 3105 has a different layout of registers 81, 85 and 86 (manual section 6.3.20): bit 7 of register 81 is setup mode, bit 6 compression, bit 5 traction, bit 4 overload or saturation, and registers 85 and 86 hold the compression/traction value instead of the tare. This map follows the layout of section 6.3.7.
• The manual gives the response of the status block as 12 bytes in section 6.3.7 and 18 bytes in section 6.3.20; six registers are 12 bytes.
• Registers 231, 251, 271 and 851 are documented for writing only (the response repeats the value sent), so they are marked W. The device address is limited to 0 to 99 when programmed, while the protocol allows 0 to 247.
• Serial defaults: 19200 baud, 8 data bits, no parity, 2 stop bits. Retries must be at least 100 ms apart.