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REFERENCE INFORMATION
SSLBP
NORMAL START
When the FPGA is first configured or after a STOP command, all local
communication, error and status parameters are initialized and all LBP communication
channels are idle. A normal START command begins to establish communications with
all remote LBP devices. A normal start command is issued by writing a Start bit with type
bits of 0,0,1 with a bit mask of the desired channels to start in the low byte, This is 0x9NN
hex where NN is the bitmask of channels to start. This command is written to the
command register to start the selected channels.
Once a start command has been issued, all channels that are selected in the bit
mask will be probed to determine if a LBP device exists. If a device exists on a channel,
the SSLBP firmware will acquire the device name, and device unit number, and pointers
to process data information from the remote device..
A normal start command also does a standard set of remote device setup
operations when it detects a remote device. This setup includes clearing any faults, setting
remote operational mode, and setting the outputs off. If no errors have occurred and all
faults are clearable, the SSLBP firmware enters a "chatter" loop where it repeatedly sends
output data of all 0's. This keeps the remote devices watchdog fed while waiting for the first
DOIT command.
When the command completes (the command register is clear), the data register
can be read to determine if all selected channels have started. A 1 bit in any position in the
data register indicates that the corresponding channel has failed to start. If a channel has
failed to start, more information about the failure can be determined by reading the CS
register of the failed channel.
Once a DOIT command has been executed, the firmware no longer "chatters" and
it becomes the responsibility of the host interface to continue sending DOIT commands at
a rate sufficient to feed the remote devices watchdog (faster than 20 Hz with the default
50 mS watchdog timeout period). If this is not done, the remote device’s watchdog will bite,
disabling its outputs and setting the fault flag. This will require a channel stop followed by
a channel start to resume normal operations.
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