TN8044AH-R0117 datasheet(46/65 Pages) INNOVASIC

46 / 65 page

IA8044/IA8344

Data Sheet

SDLC Communications Controller

March 30, 2010

IA211010112-04

http://www.Innovasic.com

UNCONTROLLED WHEN PRINTED OR COPIED

Customer Support:

Page 46 of 65

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Frame Option

NFCS

Frame Format

No-Control

Field

No-FCS Field

FLEXIBLE

Mode

Inf

No-Control

Field

No-Address

Field

No-FCS Field

FLEXIBLE

Mode

Inf

= Address field

= Control field

FCS = Frame check sequence

= Flag

Inf

= Information field

4.14

HDLC Restrictions

The IA8044/IA8344 supports a subset of the HDLC protocol. The differences include the

restriction by the IA8044/IA8344 of the serial data to be in 8-bit increments. In contrast, HDLC

allows for any number of bits in the information field. HDLC provides an unlimited address field

and an extended frame number sequencing. HDLC does not support loop configuration.

4.15

SIU Details

The SIU is composed of two functional blocks with each having several sub blocks. The two

blocks are called the bit processor (BIP) and the byte processor (BYP) (see Figure 11).

4.15.1 BIP

The BIP consists of the DPLL, NRZI encoder/decoder, serial/parallel shifter, zero

insertion/deletion, shutoff logic, and FCS generation/checking. The NRZI logic compares the

current bit to the previous bit to determine if the bit should be inverted. The serial shifter converts

the outgoing byte data to bit data and incoming bit data to byte data. The zero insert/delete

circuitry inserts and deletes zeros and also detects flags (01111110), go-aheads (GA) (01111111),

and aborts (1111111). The pattern 1111110 is detected as an early go-ahead that can be turned

into a flag in loop configurations. The shutoff detector is a three-bit counter that is used to detect

a sequence of eight zeros, which is the shutoff command in loop-mode transmissions. It is cleared

whenever a ―1‖ is detected. The FCS logic performs the generation and checking of the FCS

value according to the polynomial described above. The FCS register is set to all 1s prior to each

calculation. If a CRC error is generated on a receive frame, the SIU will not interrupt the CPU

and the error will be cleared upon receiving an opening flag.

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