SCC Transparent Mode
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
28-7
Table 28-4
describes receive commands.
28.7
Handling Errors in the Transparent Controller
The SCC reports message reception and transmission errors using the channel buffer descriptors, the error
counters, and SCCE.
Table 28-5
describes transmit errors.
Table 28-6
describes receive errors.
28.8
Transparent Mode and the PSMR
The protocol-specific mode register (PSMR) is not used by the transparent controller because all
transparent mode selections are made in the GSMR. If only half of an SCC (transmitter or receiver) is
Table 28-4. Receive Commands
Command
Description
ENTER
HUNT
MODE
After hardware or software is reset and the channel is enabled, the channel is in receive enable
mode and uses the first BD in the table.
ENTER
HUNT
MODE
forces the transparent receiver to the
current frame and enter hunt mode where the transparent controller waits for the synchronization
sequence. After receiving the command, the current buffer is closed. Further data reception uses
the next BD.
CLOSE
RXBD
Forces the SCC to close the RxBD if it is being used and to use the next BD for any subsequently
received data. If the SCC is not receiving data, no action is taken by this command.
INIT
RX
PARAMETERS
Initializes all receive parameters in this serial channel parameter RAM to reset state. Issue only
when the receiver is disabled.
INIT
TX
AND
RX
PARAMETERS
resets receive and transmit parameters.
Table 28-5. Transmit Errors
Error
Description
Transmitter
Underrun
When this occurs, the channel stops sending the buffer, closes it, sets TxBD[UN], and generates a
TXE interrupt if it is enabled. Transmission resumes after a
RESTART
TRANSMIT
command is received.
Underrun occurs after a transmit frame for which TxBD[L] was not set. In this case, only SCCE[TXE]
is set. Underrun cannot occur between transparent frames.
CTS Lost During
Message
Transmission
When this occurs, the channel stops sending the buffer, closes it, sets TxBD[CT], and generates the
TXE interrupt if it is enabled. The channel resumes sending after
RESTART
TRANSMIT
is received.
Table 28-6. Receive Errors
Error
Description
Overrun
The SCC maintains a receive FIFO. The CPM starts programming the SDMA channel if the buffer
is in external memory and updating the CRC when 8 or 32 bits are received in the FIFO as
determined by GSMR_H[RFW]. If a FIFO overrun occurs, the SCC writes the received byte over the
previously received byte. The previous character and its status bits are lost. Afterwards, the channel
closes the buffer, sets OV in the BD, and generates the RXB interrupt if it is enabled. The receiver
immediately enters hunt mode.
CD Lost During
Message
Reception
When this occurs, the channel stops receiving messages, closes the buffer, sets RxBD[CD], and
generates the RXB interrupt if it is enabled. This error has highest priority. The rest of the message
is lost, and no other errors are checked in the message. The receiver immediately enters hunt mode.
Summary of Contents for PowerQUICC MPC870
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