Toshiba E-STUDIO190F Service Manual page 256

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
Start De-limiter (SFD)
1 byte
P: priority
S: Status
R: Reserved
Data Frame Format
Most significant bit
SFD Access
1 byte Control
1 byte
Data: Max 4429 byte (4M)
Max 17779 (16M)
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
P P P S M R R R
0 = Token Frame
1 = Data Frame
Frame Destination
control MAC
1 byte 6 or 2 byte
Least significant bit
End De-limiter (ED)
1 byte
Source Data FCS
MAC 4 byte
6 or 2 byte
256
Least significant bit
ED Frame
1 byte Status
1 byte