
Communications Processor (CP)
MOTOROLA
MC68302 USER’S MANUAL
4-141
4.7.4.1 SMC1 Receive Buffer Descriptor
The CP reports information about the received byte using this (BD).
E—Empty
0 = This bit is cleared by the CP to indicate that the data byte associated with this BD
is now available to the M68000 core.
1 = This bit is set by the M68000 core to indicate that the data byte associated with this
BD is empty.
In GCI mode, when the IMP implements the monitor channel protocol, the IMP will wait until
this bit is set by the M68000 core before acknowledging the monitor channel data. In other
modes (transparent GCI and IDL), additional received data bytes will be discarded until the
empty bit is set by the M68000 core.
L—Last (EOM)
This bit is valid only in GCI mode when the IMP implements the monitor channel protocol.
This bit is set when the end-of-message (EOM) indication is received on the E bit.
NOTE
When this bit is set, the data byte is not valid.
ER—Error Condition
This bit is valid only in GCI mode when the IMP implements the monitor channel protocol
and the L bit is set. This bit is set when an error condition occurs on the monitor channel
protocol. A new byte is transmitted before the IMP acknowledges the previous byte.
MS—Data Mismatch
This bit is valid only in GCI mode when the IMP implements the monitor channel protocol.
This bit is set when two different consecutive bytes are received and is cleared when the
last two consecutive bytes match. The IMP waits for the reception of two identical consec-
utive bytes before writing new data to the receive BD.
Bits 11–10—Reserved for future use.
AB—Received A Bit
This bit is valid only in GCI mode when the monitor channel is in transparent mode.
EB—Received E Bit
This bit is valid only in GCI mode when the monitor channel is in transparent mode.
Data—Data Field
The data field contains the byte of data received by SMC1.
15
14
13
12
11
10
9
8
7
0
E
L
ER
MS
—
AB
EB
DATA