Command Set
All commands must be terminated by a carriage return character (ASCII $0D). In all command examples in this text the carriage return is either implied or denoted by the symbol ‘CR’.
Data Structure
Many commands require additional data values to complete the command definition as shown in the example commands in Table 4.1. The particular data necessary for these commands is described in full in the complete command descriptions.
Write Protection
Some commands listed in Table 4.1 are under the heading of ‘Write Protected Commands’. These commands are used to alter setup data in the module’s EEPROM. These commands are write protected to guard against accidental loss of setup data. All
Miscellaneous Protocol Notes
The address character must transmitted immediately after the command prompt character. After the address character the module will ignore any character below ASCII $23 (except, of course, CR). This allows the use of spaces (ASCII $20) within the command message for better readability if desired.
The length of a command message is limited to 25 printable characters. If a properly addressed module receives a command message of more than 25 characters the module will abort the whole command sequence and no response will result.
If a properly addressed module receives a second command prompt before it receives a CR, the command will be aborted and no response will result.
Response Structure
Response messages begin with either an asterisk ‘*’ (ASCII $2A) or a question mark ‘?’ (ASCII $3F) prompt. The ‘*’ prompt indicates acknowledg- ment of a valid command. The ‘?’ prompt precedes an error message. All response messages are terminated with a CR. Many commands simply return a single ‘*’ character to acknowledge that the command has been executed by the module. Other commands send data information following the ‘*’ prompt. The response format of all commands may be found in the detailed command description. The maximum response message length is 25 characters.
