GE GFK-1004B user manual Programming Communications Requests

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AChannel Command setup to issue a single send can have only one pendingsend transfer.

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 Units 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 4-1.

(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; 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 4-2.

(Word 14) Local PLC - Memory Starting Address: Word 14 specifies the starting address in the local PLC from which the data is to be sent (1-based).

GFK-1004B Chapter 4 Programming Communications Requests 4-19