Panasonic Workio DP-1520P, Service Manual

Page: 422 / 496

422
SEP 2004
Ver. 1.2
DP-1520P/1820P/1820E
A computer in the ring captures the token, if it has data to transmit, it holds the token and transmits a data
frame. This data frame is passed to each computer in the ring, which checks whether it is the intended
recipient of the frame.
When the frame reaches the destination address, the destination PC copies the frame to a receive buffer,
updates the frame status field of the data frame and puts the frame back on the ring. When the computer
that originally sent the frame receives it back from the ring, it acknowledges a successful transmission,
takes the frame off the ring, and places the token back on the ring.
Token Frame indicates that the network is available for transmission.
Data Frame indicates that the network is busy processing a transmission.
Token Frame Format
Data Frame Format
There are several different bit types assigned for Frame Status. For example, 1 and 5 bit indicates that the
token has been read, 2 and 6 bit indicates that the frame has been copied by another station. Thus, we can
confirm whether the Data Frame was delivered.
Most significant bit
Start De-limiter (SFD)
1 byte P P P S M R R R End De-limiter (ED)
1 byte
P: priority
S: Status
0 = Token Frame
1 = Data Frame
R: Reserved
Least significant bit
Most significant bit
SFD
1 byte Access
Control
1 byte Frame
control
1 byte Destination
MAC
6 or 2 byte Source
MAC
6 or 2 byte Data FCS
4 byte ED
1 byte Frame
Status
1 byte
Data: Max 4429 byte (4M)
Max 17779 (16M)
Least significant bit