UM0851 datasheet(113/245 Pages) STMICROELECTRONICS

113 / 245 page

UM0851

Communication device drivers

Doc ID 16604 Rev 2

113/245

HDLC controller features:

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Compliant with ISO/IEC13239

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Standard HDLC frame code/decode

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Tx channel features:

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Automatic Inter-Frame Fill (IFF) generation (0x7E or 0xFF)

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Automatic flag generation

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Selectable CRC generation

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Automatic contention resolution, RS485 which sends bit ‘0’ first occupies the bus.

RS485 which loses the bus will restart the frame transmitting automatically as

soon as the bus becomes idle.

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Delay between Tx data and echo data is configurable

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Priority class penalty configurable

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Rx channel feature:

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Automatic flag detection

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Programmable address recognition

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Automatic inter-frame fill (IFF) detection (0x7E or 0xFF)

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Storing CRC received into external memory is configurable

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Exception report

4.10.2

Software overview

From the software view, the programming models for the TDM/E1 HDLC and RS485 HDLC

controllers are very similar in several aspects. Both of them use similar DMA descriptor

structure, similar interrupt queue and so on. So TDM/E1 HDLC and RS485 HDLC share the

same driver code in Linux

There is a generic HDLC layer in the Linux kernel. The general HDLC layer for Linux is an

interface between low-level hardware drivers for synchronous serial (HDLC) cards and the

rest of kernel networking. It exposes the HDLC interface as a network device. With this

design, it is very easy to use and test the HDLC interface

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