DS26401 datasheet(134/309 Pages) DALLAS

134 / 309 page

DS26401 Octal T1/E1/J1 Framer

134

THC1

Transmit HDLC Control Register 1

110h + (200h x n) : where n = 0 to 7, for Ports 1 to 8

Bit #

Name

NOFS

TEOML

THR

THMS

TFS

TEOM

TZSD

TCRCD

Default

Bit 0 / Transmit CRC Defeat (TCRCD).

A 2-byte CRC code is automatically appended to the outbound message.

This bit can be used to disable the CRC function.

0 = enable CRC generation (normal operation)

1 = disable CRC generation

Bit 1 / Transmit Zero Stuffer Defeat (TZSD).

The Zero Stuffer function automatically inserts a zero in the message

field (between the flags) after 5 consecutive ones to prevent the emulation of a flag or abort sequence by the data

pattern. The receiver automatically removes (de-stuffs) any zero after 5 ones in the message field.

0 = enable the zero stuffer (normal operation)

1 = disable the zero stuffer

Bit 2 / Transmit End of Message (TEOM).

Should be set to a one just before the last data byte of an HDLC packet

is written into the transmit FIFO at THF. If not disabled via TCRCD, the transmitter will automatically append a 2-

byte CRC code to the end of the message.

Bit 3 / Transmit Flag/Idle Select (TFS).

This bit selects the inter-message fill character after the closing and

before the opening flags (7Eh).

0 = 7Eh

1 = FFh

Bit 4 / Transmit HDLC Mapping Select (THMS)

0 = Transmit HDLC assigned to channels

1 = Transmit HDLC assigned to FDL(T1 mode), Sa Bits(E1 mode)

Bit 5 / Transmit HDLC Reset (THR).

Will reset the transmit HDLC controller and flush the transmit FIFO. An abort

followed by 7Eh or FFh flags/idle will be transmitted until a new packet is initiated by writing new data into the FIFO.

Must be cleared and set again for a subsequent reset.

0 = Normal operation

1 = Reset transmit HDLC controller and flush the transmit FIFO

Bit 6 / Transmit End of Message and Loop (TEOML).

To loop on a message, should be set to a one just before

the last data byte of an HDLC packet is written into the transmit FIFO. The message will repeat until the user clears

this bit or a new message is written to the transmit FIFO. If the host clears the bit, the looping message will

complete then flags will be transmitted until new message is written to the FIFO. If the host terminates the loop by

writing a new message to the FIFO the loop will terminate, one or two flags will be transmitted and the new

message will start. If not disabled via TCRCD, the transmitter will automatically append a 2-byte CRC code to the

end of all messages.

Bit 7 / Number of Flags Select (NOFS)

0 = send one flag between consecutive messages

1 = send two flags between consecutive messages

DS26401 Datasheet(PDF) 134 Page - Dallas Semiconductor

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