The SZG-TST-TXR4 is a SYZYGY Transceiver peripheral intended to be used by SYZYGY carrier developers to test continuity during development or production of their carrier. It can be used during automated testing to validate connector I/O.


SYZYGY Information

Compatibility Table

Port typeSYZYGY Transceiver
5V supply requiredYes
Nominal 5V supply current< 10mA
Nominal 3.3V supply current< 10mA
VIO supply voltage1.8V
Nominal VIO supply current< 100mA
Total number of I/OUp to 18

DNA Data

This data is stored in the SYZYGY DNA microcontroller on the SZG-TST-TXR4 peripheral.

Max 5V Load10 mA
Max 3.3V Load10 mA
Max VIO Load10 mA
VIO Min1.8V
VIO Max1.8V


The source of the following pinout information is the SZG-TST-TXR4 schematic. This pinout follows the SYZYGY specification for TXR4 ports.

  • Column PIN NUM (J1) lists the pin number on the SYZYGY specification’s Transceiver Samtec connector, this is reference designator J1 in the schematic. For connections that are looped back, both pins are listed.
  • Column SIGNAL NAME lists the SYZYGY specification’s name for this pin’s connection. For connections that are looped back, both signal names are listed.
  • Column SCHEMATIC NET lists the net name found in the SZG-TST-TXR4’s schematic for the connection.
5 <-> 6 RX0p <-> TX0p LOOPBACK_0P0.01 μF AC-coupling capacitor
7 <-> 8 RX0n <-> TX0n LOOPBACK_0N0.01 μF AC-coupling capacitor
9 <-> 10 RX1p <-> TX1p LOOPBACK_1P0.01 μF AC-coupling capacitor
11 <-> 12 RX1n <-> TX1n LOOPBACK_1N0.01 μF AC-coupling capacitor
13 REFCLKp REFCLKP125 MHz reference oscillator
14 S0TEST_MODE_3_VIO (Atmel PB0, U1 pin 11)
15 REFCLKn REFCLKN125 MHz reference oscillator
16 S1TEST_MODE_2_VIO (Atmel PB1, U1 pin 12)
17 S2TEST_MODE_1_VIO (Atmel PB2, U1 pin 14)
18 S3TEST_MODE_0_VIO (Atmel PA7, U1 pin 15)
19 <-> 20 S4 <-> S5 S5_S4_LOOP
21 <-> 22 S6 <-> S7 S6_S7_LOOP
23 <-> 24 S8 <-> S9 S8_S9_LOOP
25 <-> 26 RX3p <-> TX3pLOOPBACK_3P0.01 μF AC-coupling capacitor
27 <-> 28 RX3n <-> TX3nLOOPBACK_3N0.01 μF AC-coupling capacitor
29 <-> 30 RX2p <-> TX2pLOOPBACK_2P0.01 μF AC-coupling capacitor
31 <-> 32 RX2n <-> TX2n LOOPBACK_2N0.01 μF AC-coupling capacitor
33 <-> 34 P2C_CLKp <-> C2P_CLKp LOOPBACK_CLKP
35 <-> 36 P2C_CLKn <-> C2P_CLKn LOOPBACK_CLKN


The SZG-TST-TXR4 is designed to assist carrier developers perform continuity and power supply tests during development and production testing. To accomplish this, the test peripheral connects a communication path from the FPGA to the Atmel MCU for power supply tests. The remaining pins on the connector are shorted together according to the connections in the table above to allow for continuity testing.

Test Firmware

The Atmel MCU on the test peripherals contains a modified version of the normal DNA firmware. The test firmware removes the power supply sequencing options present in the standard firmware.The test firmware also uses the AVR to measure each of the power supply rails, reporting their status back to the FPGA.

Each supply rail is measured with the internal AVR ADC and checked against a pair of threshold values corresponding to the SYZYGY specified tolerance of that power supply rail. If the supply rail is within its required tolerance the AVR sets a “good” status bit for that rail. The VIO rail is assumed to be at 1.8V by the AVR firmware and the DNA for the test peripheral. A 1.8V VIO is used to maximize compatibility with current FPGA I/O supply requirements.

Supply status is communicated back to the FPGA through SYZYGY pins 14, 16, 17, and 18. The AVR continuously reads AVR pin PA7 (SYZYGY Pin 18 (S3)), then outputs the power supply state on the PB[2:0] pins according to the table below.

    +5V Supply +3.3V Supply VIO Supply
PA7 = 1 Good PB0 = 1 PB2 = 1 PB1 = 1
Bad PB0 = 0 PB2 = 0 PB1 = 0
PA7 = 0 Good PB0 = 0 PB2 = 0 PB1 = 0
Bad PB0 = 1 PB2 = 1 PB1 = 1

By toggling the PA7 pin with the FPGA it is possible to test continuity on the MCU pins while also checking the status of each power supply.