User Manual

PLUS System Manual Reader Data Interface 61
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char toaPcnt; /* TOA status and preamble count */
};
The tagId field in the structure above will be received in reverse byte order on little endian machine
architectures (e.g., Intel-based PCs) and will need to be byte-swapped.
The Reader sends a special form of the TOA packet, called a discovery TOA packet, to the network
broadcast address after initial startup. The format of the discovery TOA packet is identical to the
normal TOA packet, except the Tag ID field is set to zero. The Reader waits a small random delay after
startup before sending the initial discovery TOA packet to avoid packet storms when many readers start
at the same time (for example, after a power outage). Also, any time the Reader does not have any
normal TOA packets to transmit in a 10 second period, it will transmit a discovery TOA packet to the
location engine’s address.
3.4.2 Commands and Responses
The Reader can be controlled by sending ASCII commands over TCP port 11001. Some commands
cause the Reader to reply with an ASCII response packet. The Reader can receive either upper case or
lower case ASCII commands, and will always respond in upper case. All command and response
packets are terminated by a carriage return-line feed combination. Specific command formats are
described below.
3.4.2.1 Reader Commands
The following table lists the commands that can be sent to a Reader to command it to perform a function.