Pin Descriptions

QSFP28 Pin Description

Pin	Symbol	Description	Pin	Symbol	Description
1	GND	Ground	20	GND	Ground
2	Tx2n	Transmitter Inverted Data Input	21	Rx2n	Receiver Inverted Data Output
3	Tx2p	Transmitter Non-Inverted Data Input	22	Rx2p	Receiver Non-Inverted Data Output
4	GND	Ground	23	GND	Grounds
5	Tx4n	Transmitter Inverted Data Input	24	Rx4n	Receiver Inverted Data Output
6	Tx4p	Transmitter Non-Inverted Data Input	25	Rx4p	Receiver Non-Inverted Data Output
7	GND	Ground	26	GND	Ground
8	ModSelL	Module Select	27	ModPrsL	Module Present
9	ResetL	Module Reset	28	IntL	Interrupt
10	Vcc Rx	+3.3V Power Supply Receiver	29	Vcc Tx	+3.3V Power Supply Transmitter
11	SCL	2-wire Serial Interface Clock	30	Vcc1	+3.3V Power Supply
12	SDA	2-wire Serial Interface Data	31	LPMode	Low Power Mode
13	GND	GND	32	GND	Ground
14	Rx3p	Receiver Non-Inverted Data Output	33	Tx3p	Transmitter Non-Inverted Data Input
15	Rx3n	Receiver Inverted Data Output	34	Tx3n	Transmitter Inverted Data Input
16	GND	Ground	35	GND	Ground
17	Rx1p	Receiver Non-Inverted Data Output	36	Tx1p	Transmitter Non-Inverted Data Input
18	Rx1n	Receiver Inverted Data Output	37	Tx1n	Transmitter Inverted Data Input
19	GND	Ground	38	GND	Ground

Pin	Connector Pin Name	Port A Signal Name
1	VeeT	Module Transmitter Ground
2	Tx_Fault	Module Transmitter Fault
3	Tx_Disable	Transmitter Disable. Turns off transmitter laser output
4	SDA	2-wire Serial Interface Data Line
5	SCL	2-wire Serial Interface Clock
6	Mod_ABS	Module Absent. Grounded within the module
7	RS0	Rate Select 0, optionally controls SFP+ module receiver
8	Rx_LOS	Receiver Loss of Signal Indication
9	RS1	Rate Select 1, optionally controls SFP+ module transmitter
10	VeeR	Module Receiver Ground
11	VeeR	Module Receiver Ground
12	RD-	Receiver Inverted Data Output
13	RD+	Receiver Non-Inverted Data Output
14	VeeR	Module Receiver Ground
15	VccR	Module Receiver Power Supply
16	VccT	Module Transmitter Power Supply
17	VeeT	Module Transmitter Ground
18	TD+	Transmitter Non-Inverted Data Input. AC coupled
19	TD-	Transmitter Inverted Data Input. AC coupled
20	VeeT	Module Transmitter Ground

The below details the status/control signals interconnection between QSFP and the SFP connectors.

SFP to QSFP Status/Control Signals

QSFP Signal	SFP Signal	Description of Function
ModPrsL	ModAbs	Connected to Vee inside the SFP transceiver.
IntL	Rx_LOS	Inverted logic: IntL = Rx_LOS OR Tx_FAULT
IntL	Tx_Fault	Inverted logic: IntL = Rx_LOS OR Tx_FAULT
ModSelL		Used for encoding of the mutual exclusive SCL/SDA switch enable logic as shown below.
LPMode	RS0	Inverted logic: RS0 = RS1 = NOT LPMode
LPMode	RS1	Inverted logic: RS0 = RS1 = NOT LPMode
ResetL	Tx_Disable	Inverted logic: Tx_Disable = NOT ResetL
SCL	SCL	Connected to mutual exclusive bidirectional switches using the encoding shown in below.
SDA	SDA	Connected to mutual exclusive bidirectional switches using the encoding shown in below.

SFP to QSFP (Patented U.S. Pat. 7,934,959)

The mutually exclusive SDA/SCL connections to the QSA EEPROM and SFP module are controlled by the ModSelL and ResetL signals: