QT2022/32 - Data Sheet: DS3051
8.4.2 Receive Loss-of-Signal Pin (LOSOUTB)
LOSOUTB indicates when the input signal applied at RXIN/P is below a threshold which can be adjusted via the
resistor connected to the ITH_LOS pin. LOSOUTB=0 indicates that the signal is below the threshold.
The logic of the LOSOUTB output may be reversed using the XFP input. This may be required when using the
QT2022/32 in conjunction with an XFP module. See Section 8.2.2 for details.
8.4.3 Laser Driver Enable Pin (TXENABLE)
The TXENABLE Status Pin is used to enable or disable an external laser driver. The state of the XFP Control pin
inverts the logic TXENABLE output logic.
When XFP is LOW, the TXENABLE output is non-inverted. In the enable state, the open drain output is off allowing
an external pull-up resistor to pull the TXENABLE output high. In this state, a driver on another device may pull the
external TXENABLE signal low to disable the laser driver. In the disable state, the open drain output is on pulling
the TXENABLE output low.
When XFP is HIGH, the TXENABLE output is inverted. In the disable state, the open drain output is off allowing an
external pull-up resistor to pull the TXENABLE output high. In this state, a driver on another device may pull the
external TXENABLE signal low to enable the laser driver. In the enable state the open drain output is on, pulling the
TXENABLE output low. This pin should be connected to the XFP module “TX_DIS” pin.
The truth table showing the TXENABLE logic when XFP =0 is presented in Table 30. The truth table when XFP =1
is presented in Table 31. Note that the TXON pin state is not in the truth table in XFP mode because its function is
changed to an output.
Table 30: TXENABLE Logic (XFP = 0)
0
x
x
x
x
1
x
1
x
x
x
0
x
x
1
x
x
0
x
x
x
1
x
0
x
x
x
x
1
0
Disabled
Disabled
Disabled
Disabled
Disabled
Enabled
Low
Low
Low
Low
Low
Float
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