Installation manual

Publication 1747-RM001G-EN-P - November 2008
SLC Communication Channels 13-67
Channel 0
System
Polling Mode Message
Based
If you want to accept unsolicited messages from slave stations, choose MESSAGE BASED
(ALLOW SLAVES TO INITIATE MESSAGES)
Slave station-initiated messages are acknowledged and processed after all master
station-initiated (solicited) messages.
Note: Slave stations can only send messages when they are polled. If the message-based
master station never sends a slave station a message, the master station will never send the
slave station a poll. Therefore, to regularly obtain a slave station-initiated message from a
slave station, you should choose to use standard communication mode instead.
Ignore unsolicited messages from slave stations, choose MESSAGE BASED (DO NOT ALLOW
SLAVES TO INITIATE MESSAGES)
Slave station-initiated messages are acknowledged and discarded. The master station
acknowledges the slave station-initiated message so that the slave station removes the
message from its transmit queue, which allows the next packet slated for transmission into
the transmit queue.
Duplicate
Packet Detect
Checked Duplicate Detect lets the SLC detect if it has received a message that is a duplicate of its
most recent message from another station. If you choose duplicate detect, the processor will
acknowledge (ACK) the message but will not act on it since it has already performed the
message’s task when it received the command from the first message.
If you want to detect duplicate packets and discard them, leave this parameter checked. If
you want to accept duplicate packets and execute them, uncheck this parameter.
Reply
Message Wait
Time
1 Define the amount of time in 20 millisecond increments that the master station will wait
after receiving an ACK (to a master-initiated message) before polling the slave station for a
reply.
Choose a time that is, at minimum, equal to the longest time that a slave station needs to
format a reply packet. This would typically be the maximum scan time of the slave station.
ACK Timeout 50 The amount of time in 20 millisecond increments that you want the processor to wait for an
acknowledgment to the message it has sent before the processor retries the message or the
message errors out. This timeout value is also used for the poll response timeout.
RTS Off Delay 0 Defines the amount of time in 20 millisecond increments that elapses between the end of
the message transmission and the de-assertion of the RTS signal. This time delay is a buffer
to make sure that the modem has transmitted the message but should normally be left at
zero. See page 13-89 for further guidelines for setting this parameter.
RTS Send
Delay
0 Defines the amount of time in 20 millisecond increments that elapses between the assertion
of the RTS signal and the beginning of the message transmission. This time allows the
modem to prepare to transmit the message. The Clear-to-Send (CTS) signal must be high for
transmission to occur.
Pre-Transmit
Delay
0 Defines the amount of time in 1 millisecond increments that elapses between when the
processor has a message to send and when it asserts the RTS signal (if handshaking is
selected) or begins transmitting (if no handshaking is selected).
Message
Retries
3 Defines the number of times a master station retries a message before it declares the
message undeliverable. A poll packet is transmitted prior to each message retry.
Table 13.20 Define these parameters when configuring a SLC 5/03, 5/04, or 5/05 processor as a master station using
message-based polling mode to communicate with slave stations. (Continued)
Tab Parameter Default Selections