Installation manual

Publication 1747-RM001G-EN-P - November 2008
SLC Communication Channels 13-59
Polling Mode Message Based If you want to receive:
• only one message from a slave station per its turn, choose
STANDARD (SINGLE MESSAGE TRANSFER PER NODE
SCAN). Choose this method only if it is critical to keep the
poll list scan time to a minimum.
• as many messages from a slave station as it has, choose
STANDARD (MULTIPLE MESSAGE TRANSFER PER NODE
SCAN).
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.
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.
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
either 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 either:
• a message before it declares the message undeliverable.
• or a poll packet to an active station before the master station
declares that station to be inactive.
A poll packet is transmitted prior to each message retry.
Priority Polling Range
– High
0 Select the last slave station address to priority poll.
Priority Polling Range
– Low
255 Select the first slave station address to priority poll. Entering 255
disables priority polling.
Table 13.17 Define these parameters when configuring a SLC 5/03, 5/04, or 5/05 processor as a master station using standard
polling mode to communicate with slave stations (Continued)
Tab Parameter Default Selections