Using 2.5Gbps SerDes with Built-In Bit-Error Rate Test Circuitry Makes Measuring Link Quality Easy
- MAX9259 and MAX9260 EV kits
- Agilent® 33250A arbitrary waveform generator or similar device for clock generation
- USB cable
- Shielded twisted-pair cable with Rosenberger connectors
- Agilent DSO81004B or similar high-bandwidth digital oscilloscope
- Tektronix® P6248 differential probes or similar probes
Figure 1. MAX9259/MAX9260 EV kits with 15m STP cable bench setup.
Built-In BER Test
|Table 1. 15m, 32-Bit BER vs. PCLK Frequency for 1.1dB or 10.5dB Preemphasis and 9.4dB Equalization Settings|
|Input PCLK Frequency (MHz)||Errors at 1.1dB Preemphasis||Errors at 10.5dB Preemphasis|
Activating the PRBS Mode
- Verify that the EV kit boards, software, and drivers are properly installed and operating by running through the Quick Start procedures as discussed in the MAX9259EVKIT/MAX9260EVKIT data sheets.
- Verify that all the jumpers are set in the following positions, as shown in Table 2.
Table 2. MAX9259/MAX9260 EV Kits Jumper Settings for PRBS Test Jumper Signal Shunt Position Description JU1 CDS 2-3 CDS = low; ECU attached to MAX9259; connect USB to MAX9259 EV kit SW1 MS 2-3 (toggle switch down) MS = low; half-duplex base mode; required when writing to device registers or when using an external I²C peripheral JU2 BWS 1-2 BWS = high for 32-bit bus mode JU3 ES 2-3 ES = low JU4 DRS 2-3 DRS = low for parallel input data rates of 12.5MHz to 78MHz (32-bit bus mode) JU5 SSEN 2-3 SSEN = low JU6 PWDN 1-2 PWDN = high JU7 AUTOS 2-3 AUTOS = low JU8 H1 odd pins 2-3 2-3 H1 odd-numbered pins connect to GND JU9 BUS power 1-2 J1 pin 1, J4 pin 1, and J5 pin 1 connect to VIN JU10 BUS power 1-2 J1 pin 1, J4 pin 1, and J5 pin 1 connect to USB 5V JU21 AVDD 1-2 AVDD power from 1.8V LDO U2, powered by VIN JU22 DVDD 1-2 DVDD power from 1.8V LDO U2, powered by VIN JU23 IOVDD 1-2 1-2 IOVDD power from 1.8V LDO U2, powered by VIN
- Connect the STP cable from MAX9259 EV kit connector J1 to MAX9260 EV kit connector J1.
- Connect the parallel data source or arbitrary waveform generator output to header H1-62, PCLK_IN. Set the parallel data source frequency between 12.5MHz to 78MHz and enable the output.
- Connect the USB cable from the PC to the MAX9259 EV kit.
- Verify that MAX9259 EV kit LED120 lights up, indicating that the microcontroller is powered and enabled.
- Verify that MAX9260 EV kit LED120 lights up, indicating that the microcontroller is powered and enabled.
- Verify that MAX9260 EV kit LED2 lights up, indicating that the link has been successfully established. If LED2 is off or LED1 is on, double-check that the PCLK_IN signal is clocking data.
- Start the MAX9259/MAX9260 EV kit program by opening its icon in the Start | Programs menu. The EV kit software configuration window appears as shown in Figure 2.
- Press the Connect button and the configuration window disappears.
Figure 2. MAX9259/60 EV kits software configuration window.
- The Read All button reads the entire MAX9259 and MAX9260 device registers. The Write All button writes all MAX9259 and MAX9260 device registers with the values shown Figure 3 and Figure 4.
Figure 3. MAX9259/MAX9260 EV kits software main window (MAX9259 tab).
Figure 4. MAX9259/MAX9260 EV kits software main window (MAX9260 tab).
- From the MAX9260 tab sheet (Figure 4), read the 8-bit error count register (0x0E) to clear the errors before the PRBS test.
- Set PRBSEN = 1 (0x04 D5) first in the MAX9259 and then the MAX9260 to start the PRBS test.
- Run the PRBS self test for the desired test time, and then set PRBSEN = 0 (0x04 D5), first in the MAX9260 tab and then the MAX9259 tab to exit the PRBS self test.
- Read 8-bit error count register (0x0E) in the MAX9260 tab once. The total number of bit errors will report in the window in "PRBS error counter PRBSERR." The error counter register is an 8-bit register, so the maximum number of errors that can be recorded is 255.
Figure 5. PRBS mode—eye diagram (15m cable with 1.1dB preemphasis setting).
Figure 6. PRBS mode—eye diagram (15m cable with 10.5dB preemphasis setting).