MPC8280 datasheet(782/1386 Pages) FREESCALE

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SCC Transparent Mode

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

24-8

Freescale Semiconductor

Table 24-6 describes receive errors.

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 24-6. 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.

123

456

789

Offset + 0

—

—DE

—

—CR

Offset + 2

Data Length

Offset + 4

Rx Buffer Pointer

Offset + 6

Figure 24-2. SCC Transparent Receive Buffer Descriptor (RxBD)

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