Extended Addressing
Figure 7.1 shows a very simple system but the same addressing methodmay be used to construct very large systems. Each RS-485 string may handle up to 122 addresses, and up to 14884 A2400’s may have unique addresses.
Structured Addressing
Even for a relatively small system, it can be advantageous to employ a hierarchical addressing system as used in Fig. 7.1. This is particularly true in systems that consist of many sites that are identical. From a host software standpoint, each site can be treated identically with the same module addresses, with each site having a different A2400 address.
Extended Address Syntax
The command syntax used with Extended Addressing is quite similar to the normal protocol. The Extended Address commands are initiated with a ‘{‘ character (left curly brace, ASCII $7B), or a ‘}’ character (right curly brace, ASCII $7E). The ‘{‘ prompt is analogous to the ‘$’ prompt in that it returns the shortest possible response to complete the command. The ‘}’ prompt is similar to the ‘#’ prompt in that the command is echoed and a checksum is generated along with the other data necessary to complete the response. The ‘*’ response prompt is used in all command forms.
The Extended Address commands use a
Command examples with Extended Address ‘01’:
Command: | {01WE |
|
Response: | * |
|
Command: | }01WE |
|
Response: | *01WE27 |
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Command: | {01RS |
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Response: | *31070000 | (typical) |
Command: | }01RS |
|
Response: | *01RS31070000BB | (typical) |
Checksums may be appended to commands:
Command: {01WE78
Response: *