Datasheet

Command Processing
2-10 C141-C008
(1) Signal Interchanges on the FC Loop
a. Acquisition of loop use rights
The IDD performs arbitration with the other devices on the loop in order to
use the loop. Arbitration is accomplished by setting its own ALPA in the
ARB primitive and outputting it in the form ARB (ALPA, ALPA).
Other devices connected to the loop output the ARB primitive they have
received as the CFW (Current Fill Word) as long as they have no requests.
If the ARB (ALPA, ALPA) travels around the loop and returns to the device
which output it, then that device acquires the loop use rights.
b. Establishing connections with the destination device where data are to be
transferred
A device which has acquired loop use rights outputs the OPN primitive to
establish connections with the destination device where data are to be
transferred.
Ordinarily, many of the OPN primitives that are used are of two types, Full
Duplex Open and Half Duplex Open, and are distinguished by the ALPA
which sets the OPN primitive.
Full Duplex Open: OPN (ALPD, ALPS)
ALPD = ALPA of destination device where data are to be transferred.
ALPS = ALPA of source device which is transferring data.
Half Duplex Open: OPN (ALPD, ALPD)
ALPD = ALPA of destination device where data are to be transferred.
ALPS = ALPA of source device which is transferring data.
This IDD responds to the OPN primitive when received by both Full and Half
Duplex communications, the OPN primitive issued by this IDD is sent by
Full Duplex Open communications.
The device that receives the OPN primitive sends the R_RDY primitive if
there is allowance for storage of frames in its Buffer and informs the transfer
source device that reception is possible.
If the transfer destination device cannot receive, it sends the CLS primitive.
The transfer source device receives the CLS primitive, then it resends the
CLS primitive and releases its loop use rights.
In the case of a device which uses Full Duplex Open, while connections are
established, since it is possible to receive other frames from the transfer
destination device, it can send the OPN primitive, followed by the R_RDY
primitive to newly inform the source device that reception is possible and that
data equal in volume to its buffer size can be output. (In the example, it
shows that it is possible for it to receive 2 frames and outputs two R_RDY
primitives.)