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--- spark_abacus [2017/01/23 14:18] – [Orange Pi] software kingkevin
+++ spark_abacus [2017/01/23 18:20] – add SDM120 kingkevin
@@ Line 50: / Line 50: @@
 There is also the DDM100TCR model with an RS-485 interface, but I couldn't find any documentation about the protocol messages, thus I wasn't interested in this feature.
+===== Eastron SDM120-Modbus =====
+The [[http://www.eastrongroup.com/|Eastron]] [[http://eastrongroupco.hk02.057321.com/productsview/14.html|SDM120-Modbus]] is a slim 1-phase 2-wire electricity meter.
+Be aware as numerous SDM120 models exist, combining following options:
+  * in-line current measurement or using a current sensing coil (CT)
+  * with electro-mechanical display or LCD, sometimes with backlight
+  * only with 2 pulse outputs, or with additional MBus or Modbus interface
+I chose the {{:spark_abacus:sdm120-modbus_user_manual_scan.pdf|SDM120 model}} (one per phase) since I wanted to learn about the RS-485 interface and Modbus protocol.
+The [[http://eastrongroupco.hk02.057321.com/data/uploads/Eastron_SDM120-Modbus_protocol_V2_3_(1).pdf|corresponding Modbus document]] ({{:spark_abacus:sdm120-modbus_protocol_v2.1.pdf |older v2.1}}) lists the registers containing the measurements (input registers) and configuration (holding registers).
+This document also explains the Modbus protocol, but I rather recommend to read the one for the [[http://eastrongroupco.hk02.057321.com/data/uploads/Eastron_SDM630MV_CT_protocol_V1_0_.pdf|SDM630]] since it contains more information, most importantly the timing between messages.
 ====== EPS8266 ======