Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-337
SCC2
COMMUNICATION
16
PROCESSOR
MODULE
DEF—Defer Indication
This bit indicates that this frame had a collision before it was sent. It is useful for channel
statistics. The SCC2 Ethernet controller writes this bit after it finishes transmitting the
associated data buffer.
HB—Heartbeat
This bit indicates the collision input was not asserted within 20 transmit clocks after
transmission. It cannot be set unless the HBC bit is set in the PSMR–SCC2 Ethernet. The
SCC2 Ethernet controller writes this bit after it finishes transmitting the associated data
buffer.
LC—Late Collision
This bit indicates that a collision occurred after the number of bytes defined for the LCW bit
in the PSMR–SCC2 Ethernet are transmitted. The SCC2 Ethernet controller stops
transmitting and writes this bit after it finishes transmitting the associated data buffer.
RL—Retransmission Limit
This bit indicates when the transmitter fails Retry Limit + 1 attempts to successfully transmit
a message because of repeated collisions on the medium. The SCC2 Ethernet controller
writes this bit after it finishes transmitting the associated data buffer.
RC—Retry Count
These bits indicate the number of retries required before this frame is successfully
transmitted. If RC = 0, then the frame is transmitted correctly the first time. If RC = 15 and
RET_Lim = 15 in the parameter RAM, then 15 retries are required. If RC = 15 and
RET_Lim > 15 in the parameter RAM, then 15 or more retries are required. The SCC2
Ethernet controller writes these bits after it finishes transmitting the associated data buffer.
UN—Underrun
This bit indicates that the SCC2 Ethernet controller has encountered a transmitter underrun
condition while transmitting the associated data buffer. The SCC2 Ethernet controller writes
this bit after it finishes transmitting the associated data buffer.
CSL—Carrier Sense Lost
This bit indicates that the carrier sense was lost during frame transmission. The SCC2
Ethernet controller writes this bit after it finishes transmitting the associated data buffer.
DATA LENGTH
This field represents the number of octets the SCC2 Ethernet controller should transmit from
this buffer descriptor data buffer. It is never modified by the communication processor
module. The value of this field should be greater than zero. The SCC2 Ethernet controller
writes these bits after it finishes transmitting the associated data buffer.
TX DATA BUFFER POINTER
This field contains the address of the associated data buffer, can be even or odd, and reside
in internal or external memory. This value is never modified by the communication processor