User's Manual

A PPENDIX B – U NDERSTANDING THE

BROADCAST OPTION IN RS-485 B ASED N ETWORKS

Appendix B – Understanding the BROADCAST option in

RS-485 Based Networks

The BROADCAST feature allows a command to be sent to ALL units connected on the

same PC COMM Port. Using a NETWORK ID of –1 enables “Broadcast Mode”. Although

this is often a very convenient feature, it also has some inherent issues that the user should

be aware of and understand. Bioscrypt recommends that only advance users attempt the

BROADCAST features.

NO REPLIES. When in Broadcast mode, no replies from the receiving unit are possible.

This is because that since all units receive the command at the same time, all units would

then normally reply at the same time. On a RS485 network, it more then one unit is

communicating at the same time, the communications electrically collide and cannot be

understood. This is an inherent shortcoming of the RS485 protocol. This collision will also

happen if 2 or more units are the same NETWORK ID, since they will both respond at the

same time and cause the same problem. When in Broadcast mode, the Bioscrypt readers

are instructed NOT to REPLY.

NO ERROR CHECKING. The Bioscrypt communication protocol has various error

checking methods built into the interface. This error checking requires two-way

communication between the PC and the Bioscrypt reader to ensure that command packets

where received and all data contained. Because NO REPLIES are possible, the error

checking is disabled in Broadcast mode.

This can become an issue when using a network of Bioscrypt readers since the reader itself

cannot process a communication packet during Verification. Although this time is very

short, if a command is received during portions of a Verification the unit would normally

respond with a BUSY error code. However, if in Broadcast mode, no response can be

given and the VeriAdmin will not know that the command was ignored by that particular unit

(even though it would have been accepted by all other units.) Manual verification is often

required to ensure all units successfully received a Broadcast command. An example of

this can be seen in the BROADCAST PC TEMPLATE section. The VeriAdmin Software will

Broadcast the TRANSFER command, but then manually verify that the template was

successfully transferred to each and every unit after the Broadcast command is complete.

Since Broadcast commands cannot have the Bioscrypt reader reply, using a Network ID

has been disabled in Reset to Factory defaults and Sensor Settings.

NOTE: A Broadcast command will be received by all units on the same PC COMM port. If

a network consists of multiple COMM ports, the Broadcast command will have to be sent on

each COMM port in order to reach all units on the network. This is automatically done by

the VeriAdmin Software for BROADCAST PC TEMPLATES and for all commands in the

BROADCAST PARAMETERS window based on the UNITIDS.DAT file. However, this is

not for other commands where the user specifies a Network ID of –1.