MPC8280 datasheet(815/1386 Pages) FREESCALE

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SCC AppleTalk Mode

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

26-3

Figure 26-2. Connecting the MPC8280 to LocalTalk

The 16

× overspeed of a 3.686-MHz clock can be generated from an external frequency source or from one

of the baud rate generators if the resulting output frequency is close to a multiple of the 3.686 MHz

frequency. The MPC8280 asserts RTS throughout the duration of the frame so that RTS can be used to

enable the RS-422 transmit driver.

26.4

Programming the SCC in AppleTalk Mode

The AppleTalk controller is implemented by setting certain bits in the HDLC controller. Otherwise,

Chapter 22, “SCC HDLC Mode,” describes how to program the HDLC controller. Use GSMR, PSMR, or

TODR to program the AppleTalk controller.

26.4.1

Programming the GSMR

Program the GSMR as described below:

1. Set MODE to 0b0010 (AppleTalk).

2. Set DIAG to 0b00 for normal operation, with CD and CTS grounded or configured for parallel I/O.

This causes CD and CTS to be internally asserted to the SCC.

3. Set RDCR and TDCR to (0b10) a 16

× clock.

4. Set the TENC and RENC bits to 0b010 (FM0).

5. Clear TEND for default operation.

6. Set TPP to 0b11 for a preamble pattern of all ones.

7. Set TPL to 0b000 to transmit the next frame with no synchronization sequence and to 001 to

transmit the next frame with the LocalTalk synchronization sequence. For example, data frames do

not require a preceding synchronization sequence. These bits may be modified on-the-fly if the

AppleTalk protocol is selected.

Two HDLC

CRC-16

Flags

Destination

Address

Data

Control

Byte

6-Bit Sync

Sequence

Source

Address

Closing

Flag

16 Ones

(Abort)

RS-422

TXD

RTS

RXD

Stored in Receive Buffer

Standard HDLC frame handling

MINI-DIN 8

Stored in Transmit Buffer

SCC

RTS

TXD

Tx Data

Tx Enable

Rx Data

MPC8280

Connection

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