Irda Mode—Scc2 Only; Asynchronous Hdlc Features - Freescale Semiconductor MPC850 User Manual

Chapter 25
SCC Asynchronous HDLC Mode and
IrDA
Asynchronous HDLC and IrDA uses HDLC framing techniques with UART-type
characters. This document refers to both protocols collectively as asynchronous HDLC.
The asynchronous HDLC protocol is typically used as the physical layer for point-to-point
protocol (PPP) and the infrared link access protocol (IrLAP). Although asynchronous
HDLC can be implemented in conjunction with the core, it is more efficient and less
computationally intensive to let the CPM handle framing and transparency functions. For
further information on the implementation of IrDA on the MPC850 see Chapter 29, "IrDA
Mode—SCC2 Only."
The RFC 1549 octet stuffing/unstuffing provided by this mode supports only asynchronous
transmission. This mode cannot be used to provide octet stuffing for synchronous
communication lines.

25.1 Asynchronous HDLC Features

The following list summarizes the main features of the SCC in asynchronous HDLC mode:
• Flexible buffer structure lets all or part of a frame be sent or received
• Separate interrupts for received frames and transmitted buffers
• Automatic CRC generation and checking
• Support for nonmultiplexed serial interface control signals
• Automatic generation of opening and closing flags
• Reception of frames with a single shared flag
• Automatic generation and stripping of transparency characters according to RFC
1549 using transmit and receive control character maps
• Programmable opening flag, closing flag, and control escape characters
• Automatic transmission of the abort sequence after a
• Automatic transmission of idle characters between frames and between characters
Chapter 25. SCC Asynchronous HDLC Mode and IrDA
command
STOP TRANSMIT