Freescale Semiconductor MPC8260 - Manual (Page 778)

SCC Transparent Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
24-8 Freescale Semiconductor
24.9 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
running the transparent protocol, the other half (receiver or transmitter) can support another protocol. In
such a case, use the PSMR for the non-transparent protocol.
24.10 SCC Transparent Receive Buffer Descriptor (RxBD)
The CPM reports information about the received data for each buffer using an RxBD, closes the current
buffer, generates a maskable interrupt, and starts receiving data into the next buffer after one of the
following occurs:
• An error is detected.
• A full receive buffer is detected.
• An ENTER HUNT MODE command is issued.
• A CLOSE RXBD command is issued.
Figure 24-2 displays an SCC transparent receive buffer descriptor.
Table 24-7 describes RxBD status and control fields.
Table 24-6. 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.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Offset + 0 E — W I L F CM — DE — NO — CR OV CD
Offset + 2 Data Length
Offset + 4 Rx Buffer Pointer
Offset + 6
Figure 24-2. SCC Transparent Receive Buffer Descriptor (RxBD)