Motorola MC68838 User Manual page 29

The kind of token released is specified by the token send field in the packet
request header of the last FSI frame sent with this token, or is the kind of token
captured if no FSI frames were sent. The MAC then purges all frames until one of
the following occurs:
A special void frames returns,
A nonduplicate token returns,
RING_OPERATIONAL becomes low,
The transmitter enters the FDX states, or
The MAC is turned off (MAC_ON = 0).
Purging does not stop if a duplicate token is received (i.e., a token received while
transmitting). Purging differs from stripping in that purging creates no frame
fragments.
FDX_MODE—Enable Full-Duplex Operation
0 = The transmitter operates purely in ring mode.
1 = The next time the transmitter enters the Tx_Idle (T0) state, it transitions to the
FDX_Idle state. The transmitter then alternates between the FDX_Idle and
FDX_Data states, depending on whether or not there is a frame to send. The
transmitter leaves FDX_Idle or FDX_Data upon:
Receiving a higher or lower claim frame,
Receiving any beacon frame,
Receiving a MAC_RESET (RESET_FIELD <> 00), or
Clearing this bit, which puts the transmitter in the FDX_Idle state.
RING_OPERATIONAL (which could be either zero or one) is ignored while in the
FDX states. RING_OPERATIONAL is cleared upon leaving the FDX states
unless these states are left because FDX_MODE is cleared.
FDX_MODE is useful in implementing point-to-point links and for diagnostics.
BRIDGE_STRIP—Use Bridge/Switch Stripping Algorithm
0 = The normal stripping algorithm is used, based upon matching the SA against my
short address register, my long address register, and the CAM entries.
1 = An additional stripping occurs when the count of frames sent minus frames
received (called SENT_COUNT) is greater than zero. SENT_COUNT is also
cleared (hence, stripping stops) when:
A special void frame (FC = 48-bit addressed void frame) is received.
Individual DA is matched (A_FLAG = 1 and the l/G bit of the DA = 0).
SA is matched (M_FLAG = 1—i.e., SA = my long address register and
SA<> null) and frame has a valid CRC, length, and E-indicator (E_FLAG = 0.
A claim frame is received.
A beacon frame is received.
A token is received.
MOTOROLA MC68838 USER'S MANUAL 3-9