
DS26401 Octal T1/E1/J1 Framer
248
Register Name:
THC1
Register Description:
Transmit HDLC Control Register 1
Register Address:
110h + (200h x n) : where n = 0 to 7, for Ports 1 to 8
Bit #
7
6
5
4
3
2
1
0
Name
NOFS
TEOML
THR
THMS
TFS
TEOM
TZSD
TCRCD
Default
0
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 (destuffs) 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