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
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
74MUX ATTACH
71ADDRESS
NOTE:
ALL ADDRESSES 65 ... 79
ARE RESERVED AT ANY PORT CONFIGURED IN THE
70
65
64
RESERVED
DIRECT
ATTACH
`SILENT MASTER' MODE.
ADDRESS
1
0RESERVED
Figure 7 Bridge Multiplexer Address Conversion
20 Device Addressing and Message Routing
890 USE 103 00
