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2.2 Modbus Address Conversion

Programmable Port Models

￿or the programmable models, the user application stored in the BM85 defines the addressing conventions to be used between the serial ports and Modbus Plus. The application program must define the routing between serial ports, as well as the paths to Modbus Plus nodes.

Modbus Port Models

￿or the Modbus port models, address conversion between Modbus and Modbus Plus addresses is provided internally as described below. ￿xamples are shown in Section 2.3.

When the BM85 receives a message at a Modbus port, the Modbus address (1 ... 255) is compared to an internal address map for that port. You define the map table during your BM85 configuration. It can hold up to 64 Modbus addresses, each pointing to a five-byte routing path.

￿￿￿n ￿￿￿￿￿ss m￿￿￿￿ ￿s ￿￿￿n￿ in the table, the five routing path bytes are applied to the message. If the first byte is in the range 1 ... 64, the message is routed out on Modbus Plus. If the first byte is zero, the message goes to a Modbus port (1 ... 4) specified in byte two. If that port has a single slave device, the remaining three bytes are zeros. If the port has a network of slave devices, byte three specifies the slave address.

255	IMPLICIT
	ATTACH
	ADDRESS
80
79	RESERVED
75
	MUX ATTACH
74
71	ADDRESS
70	RESERVED
65
64	DIRECT
	ATTACH
	ADDRESS

1

0RESERVED

NOTE:

ALL ADDRESSES 65 ... 79

ARE RESERVED AT ANY PORT CONFIGURED IN THE `SILENT MASTER' MODE.

Figure 7 Bridge Multiplexer Address Conversion

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