Motorola MPC860 PowerQUICC, User Manual

Page: 784 / 1106

29-8 MPC860 PowerQUICC UserÕs Manual MOTOROLA
Part V. The Communications Processor Module
Table 29-4 describes receive commands.
29.8 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 29-5 describes transmit errors.
Table 29-6 describes receive errors.
29.9 Transparent Mode and the PSMR
The protocol-speciÞc 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
Table 29-4. 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 Þrst 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 29-5. 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 29-6. 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.