Motorola MC68838, User Manual

Page: 38 / 100

3- 18 MC68838 USER’S MANUAL MOTOROLA
TKN_CAPTURE—Token Has Been Captured
This event is signaled when the token is captured by the transmitter FSM. Specifically,
this bit is set when the receiver signals Token_Received, which causes the transmitter
FSM to transition from the Tx_Idle state to Tx_Data or Tx_Void state (i.e., FDDI
Transition T(02), not transitions T(10a) or T(03)).
This event is signaled even if the token was only captured because RING_PURGE is
one. The only time that this event is not signaled is when the TOKEN_TYPE field in the
packet request header indicates that no token is required.
BEACON_RCVD—MY_BEACON or OTHER_BEACON Frame Received
This bit is set when the receiver FSM signals My_Beacon or Other_Beacon. This MAC
chip requires the received E-indicator to be present and to be an R-symbol (in addition
to FDDI requirements) for My_Beacon or Other_Beacon to be signaled and for this bit to
be set.
CLAIM_RCVD—MY_CLAIM, HIGHER_CLAIM, or LOWER_CLAIM Frame Received
This bit is set when the receiver FSM signals My_Claim, Higher_Claim, or Lower_Claim.
This MAC chip requires the received E-indicator to be present and to be an R-symbol (in
addition to FDDI requirements) for My_Claim, Higher_Claim, or Lower_Claim to be
signaled and for this bit to be set.
FRAME_ERR—Frame Format Error or Locatable Frame Error Detected
This event is signaled when LOST_CT or ERROR_CT is incremented (see 3.3
Counters for definition).
FRAME_RCVD—Frame Received
When the NOTE_ALL_FRAMES bit in control register A is one, this event occurs every
time FRAME_CT is incremented. When NOTE_ALL_FRAMES is zero, this event occurs
every time FRAME_CT overflows.
DOUBLE_OVFL—Double Counter Overflow
This event indicates that some frames, format errors, or locatable errors have been lost
for counting purposes. (See MAC counter registers for descriptions of frames, format
errors, and locatable errors.) This event occurs if ERROR_CT overflows (i.e., wraps
from 63 to 0), or LOST_CT overflows (i.e., wraps from 63 to 0), or FRAME_CT
overflows (i.e., wraps from 65535 to 0) and FRAME_RCVD above is one.
When NOTE_ALL_FRAMES is one, it is possible for the DOUBLE_OVFL bit not to be
set when FRAME_CT overflows (i.e., if FRAME_RCVD is 0). Hence, it is possible to
have an incorrect frame count and no warning from the MAC.
During the cycle that this register is read (and hence cleared), FRAME_RCVD is
considered cleared. Hence if NOTE_ALL_FRAMES is 0, FRAME_CT is 65535, and a
frame is received the same cycle that this register is read/cleared, the FRAME_RCVD
bit is set, FRAME_CT wraps around to 0, and the rest of this register is cleared (e.g.,
DOUBLE_OVFL is read as zero and remains zero), which is the proper behavior.
ARCHIVE INFORMA
TION
ARCHIVE INFORMA
TION