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Advance Data Sheet
T7633 Dual T1/E1 3.3 V Short-Haul Terminator
May 1998
36
Lucent Technologies Inc.
Line Interface Unit: Transmit
(continued)
LIU Transmitter Alarms
(continued)
LIU Transmitter Driver Monitor (TDM) Alarm
The transmit driver monitor detects two conditions: a nonfunctional link due to faults on the primary of the transmit
line transformer, and periods of no data transmission. The TDM alarm (register LIU_REG0, bit 2) is the OR’d func-
tion of both faults and provides information about the integrity of the LIU transmitter signal path.
The first monitoring function is provided to detect nonfunctional links and protect the LIU transmitter from damage.
The alarm is set (TDM = 1) when one of the LIU transmitter line drivers (TTIP or TRING) is shorted to power supply
or ground, or TTIP and TRING are shorted together. Under these conditions, internal circuitry protects the LIU
transmitter from damage and excessive power supply current consumption by forcing the TTIP and TRING output
drivers into a high-impedance state. The monitor detects faults on the transformer primary side, but the transformer
secondary faults may not be detected. The monitor operates by comparing the line pulses with the transmit inputs.
After 32 transmit clock cycles, the LIU transmitter is powered up in its normal operating mode. The LIU transmitter
drivers attempt to correctly transmit the next data bit. If the error persists, TDM remains active to eliminate alarm
chatter and the transmitter is again internally protected for another 32 transmit clock cycles. This process is
repeated until the error condition is removed, and then the TDM alarm is deactivated. The TDM alarm status bit will
latch the alarm and remain set until being cleared by a read (clear on read).
The second monitoring function is to indicate periods of no data transmission. The alarm is set (TDM = 1) when 33
consecutive zeros have been transmitted. The alarm is cleared (TDM = 0) on the detection of a single pulse. This
alarm condition does not alter the functionality of the signal path.
Upon the transition from TDM = 0 to TDM = 1, a microprocessor interrupt will be generated if the TDM interrupt
enable bit TDMIE (register LIU_REG1, bit 2) is set. The reset default is TDMIE = 0.
A TDM alarm may occur when RLOOP is activated and deactivated. If the PRLALM bit is not set, then RLOOP may
activate an LOTC alarm, which will put the output drivers TTIP and TRING in a high-impedance state as described
in Loss of LIU Transmit Clock (LOTC) Alarm section on page 35. The high-impedance state of the drivers may in
turn generate a TDM alarm.
Setting the HIGHZ alarm prevention PHIZALM = 1 (register LIU_REG4, bit 4) prevents the TDM alarm from occur-
ring when the drivers are in a high-impedance state. The reset default is PHIZALM = 0.