Specifications

Allen-Bradley DF1 Driver Help

The number of attempts for master messages and polls share the same number of attempts as configured in the

device Fail after xxx successive timeouts. This attempt count is misleading in Half-Duplex mode since there

are multiple messages sent from the master in a single data request. For all intents and purposes:

Let cnAttempts = xxx in Fail after xxx successive timeouts

# attempts for master message timeout = cnAttempts

# attempts for poll timeout = cnAttempts

# attempts for request timeout = # attempts for master message timeout + # attempts for poll timeout ==

cnAttempts X 2

Source Empty and Slave Re-Poll Delay

The Allen-Bradley DF1 driver is optimized to send master messages and polls as quickly as possible to increase

data throughput. The initial slave poll will not be delayed since a delay is unnecessary. If the slave needs time to

process requests in its sink, it will be apparent in the initial poll response. It is at this time in which the driver

introduces a delay and re-polls the slave. Such a delay allows the slave time to process the request before the

next poll. This delay is configured in Channel Properties (under the Protocol tab) and is called Slave Re-Poll

Delay. The slave will be re-polled cnAttempts times.

Sink and Source Full

Both sink and source are essentially buffers and buffers have limitations. More importantly, it is possible for the

sink to fill up with requests. If this occurs, the slave will not acknowledge any master messages it receives. If

after cnAttempts the slave does not ACK the master, it is most likely the case that the slave sink is full. The driver

will then poll the slave emptying any responses the slave may have, making room for responses of the requests

that were in the full sink. This polling action will take place until the slave source is empty after cnAttempts. On

the next slave request, it is likely that the sink will be empty. If it is not, it may mean the driver is polling the slave

too quickly. If this is the case, increase the Slave Re-Poll Delay. Likewise, the slave source may also become full

and the driver will again poll the slave until the source is empty after cnAttempts.

Accepted and Discarded Slave Reponses

In the above sections, it has been mentioned that the slave is polled until the emptied. This is possible if the slave

source is full of queued up responses. On any given poll, only the response to the last master message is

accepted: all others are discarded.

Note: Slave-to-slave communication is not supported.

Radio Modem

The Radio Modem protocol is a command/reply protocol. There are no ACKs or NAKs during the request/response

procedure. This reduces the number of bytes the radio modems have to transmit and receive in order to complete

a transaction. This protocol supports full-duplex communications over a point-to-point link allowing for high

performance two-way communications between peers. It also supports master/slave communications allowing

for multi-drop configurations. Performance exceeds both Full-Duplex and Half-Duplex Protocols.