Omega A2400 User Manual
Page 56
Extended Addressing 9-4
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 two-character ASCII address,
each character may be one of 122 legal possibilities. Illegal characters are:
NULL ($00), CR ($0D), $ ($24), # ($23), { ($7B), and } ($7E).
Command examples with Extended Address ‘01’:
Command:
{01WE
Response:
*
Command:
}01WE
Response:
*01WE27
Command:
{01RS
Response:
*31070000
(typical)
Command:
}01RS
Response:
*01RS31070000BB
(typical)
Checksums may be appended to commands:
Command:
{01WE78
Response:
*