
DS26522 Dual T1/E1/J1 Transceiver 
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9.4.2 Transmit Register Definitions 
Register Name:
Register Description:
Register Address:
Bit # 
7 
Name 
NOFS 
Default 
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 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 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. This is an acknowledged reset, that is, the host need only to set the bit and the DS26522 will clear it once 
the reset operation is complete. Total time for the reset is less than 250
μ
s. 
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). This mode must be enabled with 
TCR2
.7.  
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 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 1: Transmit Zero Stuffer Defeat (TZSD).
 The zero stuffer function automatically inserts a zero in the message 
field (between the flags) after five consecutive ones to prevent the emulation of a flag or abort sequence by the 
data pattern. The receiver automatically removes (destuffs) any zero after five ones 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 
THC1
Transmit HDLC Control Register 1
110h, 310h 
6 
5 
4 
3 
2 
1 
0 
TEOML 
0 
THR 
0 
THMS 
0 
TFS 
0 
TEOM 
0 
TZSD 
0 
TCRCD 
0