GE 90-30 PLC - Manual (Page 58)

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3-25 GFK-1084B Chapter 3 Programming Communications Requests
(Word 8) Channel Number: Word 8 specifies the channel to be used for the send. This
value must be in the range of 1 to 16. If the channel is out of range, a command error
indication will be placed in the COMMREQ Status word. If the channel number is the
same as a channel already in use, the channel will be re-tasked to perform this new
command.
(Word 9) Number of Send Repetitions: Word 9 specifies the number of transfers to be
performed before automatically completing the communications request and closing the
channel. If this value is set to 1, only a single transfer will be issued. If this value is set to
0, transfers will be issued on the requested period until the channel is aborted.
(Word 10) Time Unit for Send Period: Words 10-11 together define how often the
transfer is to be performed (transfer period). Word 10 specifies the time unit such as
seconds or minutes for the send period. Word 11 specifies the number of those units.
The choices for the time units are specified in Table 3-1.
(Word 11) Number of Time Units for Send Period: Word 11 specifies the number of time
units for the send period. The send period is in effect even when the Channel
Command is setup to issue a single send.
Example Send Period Calculation: If Word 10 contains a value of 3 specifying seconds
as the time unit and Word 11 contains a value of 20, then the send period is 20 seconds.
A send will normally be issued at the start of each send period. If the pending transfer
has not completed during the send period, the Channel Error bit and Detailed Channel
Status words will be set to indicate a non-fatal period error. The pending transfer can
still complete after the period error occurs. For Channel Commands set up to issue
multiple sends, the next transfer will be issued only after the pending transfer
completes.
If the Number of Time Units is zero, a subsequent transfer will be issued as soon as the
previous transfer completes. In this case, no period errors are reported by the Channel
Error bit.
(Word 12) Timeout for Each Send: Word 12 specifies the time (in hundredths of a
second) the Ethernet Interface will wait for a send transfer to complete before setting the
Channel Error bit and Detailed Channel Status bits to indicate a non-fatal timeout error.
The transfer can still complete even after a timeout occurs. As a result, an application
can choose what to do if one occurs. If the timeout value is specified as zero, no timeout
errors will be reported.
For most applications a timeout need not be specified because the send period, in effect,
acts as a timeout. (Word 12 should be zero for no timeout.) However, there are two
special circumstances in which specifying a timeout is recommended:
When the number of time units (word 11) is zero, so that a subsequent transfer will be
issued as soon as the previous transfer completes and no period errors are reported. In
this case a timeout value can be specified so that timeout errors will be reported by the
Channel Error bit.
When the send period is very long (minutes or hours). In this case a shorter timeout
value can be specified so the application doesn’t have to wait for the send period to
expire before taking action.
(Word 13) Local PLC - Memory Type: Words 13-14 specify the location in the local PLC
from where the Ethernet Interface will get the data to be written to the remote SRTP
server. Permissible memory types are given in Table 3-2.
A Channel Command
setup to issue a single
send can have only one
pending
send transfer.