MC68HC58 Motorola, MC68HC58 Datasheet - Page 72

• Manufacturer Part Number: MC68HC58
• Description: Data Link Controller
• Manufacturer: Motorola

5.1.2.7 Load as First and Last Byte of Frame
5.1.3 RFC[1:0] — Receive FIFO Command Field
5.1.3.1 Do Nothing
5.1.3.2 Flush Byte
5.1.3.3 Flush Frame
5-6
MOTOROLA
The “load as first and last byte of frame” command indicates that the accompanying
data byte is a one byte frame. After the byte is placed in the TxFIFO buffer for trans-
mission, the TMFS in the status byte is set to %11 (TxFIFO full).
If this command is latched while a previously loaded complete frame is in the buffer
awaiting transmission, the accompanying data byte will be discarded.
If this command is latched while a previously loaded complete frame is being transmit-
ted, the accompanying data byte will be discarded.
Table 5-3 displays the RxFIFO commands.
The “do nothing” command indicates to the DLC that an RxFIFO buffer command
should not be executed.
The “flush byte” command flushes the first data byte or completion code in the RxFIFO
buffer. “Flush byte” commands cannot be queued. When there is nothing in the buffer,
no action is taken if a byte arrives after the command is latched. This is the only com-
mand that can flush a completion code.
The “flush frame” command flushes the current frame except for the completion code
generated when the frame has been completely received. If interrupts are enabled
when a “flush frame” command is executed, the receiver will only generate an interrupt
request once the completion code is at the head of the RxFIFO.
When the RxFIFO buffer is flushed, it is not completely cleared, but cycled until the
first byte in the RxFIFO buffer is a completion code.
If the command is latched when a complete frame is in the buffer, the entire frame, ex-
cept for the completion code, is flushed.
If the command is latched when there is nothing in the buffer, the next frame, except
for the completion code, is flushed.
Value
00
01
10
11
Table 5-3 RFC Field Encoding
CONTROL AND STATUS CODES
Flush frame except for completion code
Flush byte or completion code
Description
Do nothing
Reserved
TECHNICAL DATA
MC68HC58