Slc Control Program Canceling A Bt Prior To Transmission Across Rio Link - Allen-Bradley 1747-SN User Manual

SLC Control Program Cancelling a Block Transfer Prior To Transmission Across RIO Link
Control Flag
EN

TO
Status Flag
EW
ST
ER
DN
SLC Control Program Canceling a BT Prior to Transmission Across
RIO Link
In this example, the SLC control program cancels a BT that has been
pending (EW = 1, ST = 0) for a specific amount of time.
 If the timer expires before the scanner begins transmitting across
 The scanner fills in the error code field and sets the ER flag.
 The SLC control program clears the TO and EN flags. Note that
 Finally, the EW, ST (if set) and ER bits are reset.
M0 Control Information
M1 Status Information

When the SLC control program detects that the EW has set, a
timer in the SLC control program starts.
the RIO link (ST = 1), then the SLC control program will set the
TO flag. Note that the cancellation will not occur until all
previously scheduled BTs to the same logical rack have been
completed (i.e., when the ST bit would normally have been set).
Also, the ER bit is not set until any previously pending BTs to
that device have been completed. The SLC control program must
clear the EN flag to complete the BT operation. Note that
because of the asynchronous nature of cancelling a device that
has a BT in progress, the BT reply may indicate either a
successful completion or an error.
if the SLC control program later attempts to initiate another BT
and the TO flag is still set, the scanner will ignore the BT
request.
RIO Block Transfer





Publication 1747 6.6 - July 1996
5–19