Transparent Mode And The Psmr; Scc Transparent Receive Buffer Descriptor (Rxbd) - Freescale Semiconductor MPC850 User Manual

Transparent Mode and the PSMR

Error
Transmitter When this occurs, the channel stops sending the buffer, closes it, sets TxBD[UN], and generates a
Underrun TXE interrupt if it is enabled. Transmission resumes after a
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 When this occurs, the channel stops sending the buffer, closes it, sets TxBD[CT], and generates
During the TXE interrupt if it is enabled. The channel resumes sending after
Message received.
Transmission
Table 28-6 describes receive errors.
Error
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 When this occurs, the channel stops receiving messages, closes the buffer, sets RxBD[CD], and
Message generates the RXB interrupt if it is enabled. This error has highest priority. The rest of the message
Reception is lost, and no other errors are checked in the message. The receiver immediately enters hunt
mode.
28.9 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.
28.10 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
• A
CLOSE RXBD
Table 28-5. Transmit Errors
Table 28-6. Receive Errors
command is Issued.
command is issued.
MPC850 Family User's Manual
Description
RESTART TRANSMIT
RESTART TRANSMIT
Description
command is
is