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GFK-1541B Chapter 3 Programming Channel Commands 3-11
3
(Word 7) Channel Command Number:
Word 7 requests that a read channel be set up. If the
command is processed successfully, it will result in attempting the specified number of transfers
from the server to the client.
(Word 8) Channel Number:
Word 8 specifies the channel to be used for the read. This value must
be in the range of 1–32 for the Series 90-70 Ethernet Interface (Type 2) and 1–16 for the Series 90-
30 Ethernet Interfaces. If the channel number 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 retasked to perform this new command.
(Word 9) Number of Read Repetitions:
Word 9 specifies the number of reads to be performed
before automatically completing the communications request and closing the channel. If this
value is set to 1, only a single read will be issued. If this value is set to 0, reads will be issued
continuously on the requested period until the channel is aborted.
(Word 10) Time Unit for Read Period:
Words 10–11 together define how often the read is to be
performed (
read period
). Word 10 specifies the time unit such as seconds or minutes for the read
period. Word 11 specifies the number of those units. The choices for the time units are shown
below.
Value Meaning
1 hundredths of seconds (10 ms)
2 tenths of seconds (100 ms)
3 seconds
4 minutes
5 hours
Note: If Time Unit Value is 5 (hours), then the maximum usable value of Number of Time Units
is 5965.
(Word 11) Number of Time Units for Read Period:
Word 11 specifies the number of time units
for the read period. The read period is in effect even when the Channel command is setup to issue
a single read.
Example Read 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 read period is 20 seconds.
A read will normally be issued at the start of each read period. If the
pending
read transfer has
not completed during the read 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 reads, the next read transfer
will be issued only after the pending read 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 can occur.
A Channel
command set up
to issue a single
read can have
only one
pending
read transfer.