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QSFP28 Pin Description

QSFP28 Pin Description

Connector Pin NumberSymbolSignal Description
2Tx2nConnected to Port 2 lane Rx
Inverted Data 
3Tx2pConnected to Port 2 lane Rx
Non-Inverted Data 
5Tx4nConnected to Port 4 lane Rx
Inverted Data
6Tx4pConnected to Port 4 lane Rx
Non-Inverted Data
8Mod-SelLCable/Module Select
9ResetLCable/Module Reset
10Vcc Rx+3.3 V Power supply receiver
11SCL 2-wire serial interface clock
12SDA2-wire serial interface data 
14Rx3pConnected to Port 3 lane Tx
Non-Inverted Data
15Rx3nConnected to Port 3 lane Tx
Inverted Data
17Rx1pConnected to Port 1 lane Tx
Non-Inverted Data
18Rx1nConnected to Port 1 lane Tx
Inverted Data
21Rx2nConnected to Port 2 lane Tx
Inverted Data
22Rx2pConnected to Port 2 lane Tx
Non-Inverted Data
24Rx4nConnected to Port 4 lane Tx
Inverted Data
25Rx4pConnected to Port 4 lane Tx
Non-Inverted Data
27ModPrsLModule/cable Present
29Vcc Tx+3.3 V Power supply transmitter
30Vcc 1+3.3 V Power Supply
31LPModeLow Power Mode
33Tx3pConnected to Port 3 lane Rx
Non-Inverted Data
34Tx3nConnected to Port 3 lane Rx
Inverted Data
36Tx1pConnected to Port 1 lane Rx
Non-Inverted Data
37Tx1nConnected to Port 1 lane Rx
Inverted Data

Adapter Dimensions


Rear View of Module with Pin Placement 


SFP Pin Description

PinSymbol NameDescriptionNote
1VeeTModule Transmitter Ground--
2TX_FaultModule Transmitter Faulta
3TX_DisableTransmitter Disable. Turns off transmitter laser outputb
4SDA2-wire Serial Interface Data Linec
5SCL2-wire Serial Interface Clock Lined
6MOD_ABSModule Absent. Grounded within the moduled
7RS0No connection required--
8Rx_LOSLoss of Signal indication. Logic 0 indicates normal operation.d
9RS1No connection required--
10VeeRReceiver Ground (Common with Transmitter Ground)a
11VeeRReceiver Ground (Common with Transmitter Ground)a
12RD-Receiver Inverted DATA out. AC Coupled--
13RD+Receiver Non-inverted DATA out. AC Coupled--
14VeeRReceiver Ground (Common with Transmitter Ground)a
15VccRReceiver Power Supply--
16VccTTransmitter Power Supply--
17VeeTTransmitter Ground (Common with Receiver Ground)a
18TD+Transmitter Non-Inverted DATA in. AC Coupled--
19TD-Transmitter Inverted DATA in. AC Coupled--
20VeeTTransmitter Ground (Common with Receiver Ground)a
  1. TFAULT is an open collector/drain output, which should be pulled up with a 4.7k-10k Ohms resistor on the host board if intended for use. Pull up voltage should be between 2.0V to Vcc + 0.3V. A high output indicates a transmitter fault caused by either the TX bias current or the TX output power exceeding the preset alarm thresholds. A low output indicates normal operation. In the low state, the output is pulled to <0.8V.
  2. Laser output disabled on TDIS >2.0V or open, enabled on TDIS <0.8V
  3. Should be pulled up with 4.7kΩ-10kΩ on host board to a voltage between 2.0V and 3.6V. MOD_ABS pulls line low to indicate module is plugged in.
  4. LOS is open collector output. Should be pulled up with 4.7kΩ-10kΩ on host board to a voltage between 2.0V and 3.6V. Logic 0 indicates normal operation; logic 1 indicates loss of signal.

RJ45 to DB9 Harness Pinout

The RS232 harness cable (DB9 to RJ45) is supplied with the switch to connect a host PC to the Console RJ45 port of the system.

RJ45 to DB9 Harness Pinout