Maxim Integrated DS33R11 - Manual (Page 265)

DS33R11 Ethernet Mapper with Integrated T1/E1/J1 Transceiver
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Register Name: TR.H1TC, TR.H2TC
Register Description: HDLC #1 Transmit Control
HDLC #2 Transmit Control
Register Address: 90h, A0h
Bit
# 7 6 5 4 3 2 1 0
Name NOFS TEOML THR THMS TFS TEOM TZSD TCRCD
Default 0 0 0 0 0 0 0 0
Bit 7: Number of Flags Select (NOFS)
0 = send one flag between consecutive messages
1 = send two flags between consecutive messages
Bit 6: Transmit End of Message and Loop (TEOML). To loop on a message, this bit should be set to a 1 just
before the last data byte of an HDLC packet is written into the transmit FIFO. The message repeats 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
completes, then flags are transmitted until a new message is written to the FIFO. If the host terminates the loop by
writing a new message to the FIFO, the loop terminates, one or two flags are transmitted, and the new message
starts. If not disabled through TCRCD, the transmitter automatically appends a 2-byte CRC code to the end of all
messages. This is useful for transmitting consecutive SS7 FISUs without host intervention.
Bit 5: Transmit HDLC Reset (THR). Resets the transmit HDLC controller and flushes the transmit FIFO. An abort
followed by 7Eh or FFh flags/idle is 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 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 3: Transmit Flag/Idle Select (TFS). This bit selects the intermessage fill character after the closing and before
the opening flags (7Eh).
0 = 7Eh
1 = FFh
Bit 2: Transmit End of Message (TEOM). Should be set to a 1 just before the last data byte of an HDLC packet is
written into the transmit FIFO at HxTF. If not disabled through TCRCD, the transmitter automatically appends a 2-
byte CRC code to the end of the message.
Bit 1: Transmit Zero-Stuffer Defeat (TZSD). The zero-stuffer function automatically inserts a 0 in the message
field (between the flags) after five consecutive 1s to prevent the emulation of a flag or abort sequence by the data
pattern. The receiver automatically removes (destuffs) any 0 after five 1s in the message field.
0 = enable the zero stuffer (normal operation)
1 = disable the zero stuffer
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