Finisar AN-2030 - Manual (Page 17)

AN-2030: Digital Diagnostic Monitoring Interface for Optical Transceivers
F i n i s a r
9/26/02 Revision D Page 17
1
Diagnostics 2
2 wire serial bus address 1010001X (A2h) is used to access measurements of 3
transceiver temperature, internally measured supply voltage, TX bias current, TX output 4
power, received optical power, and two additional quantities to be defined in the future. 5
The values are interpreted differently depending upon the option bits set at address 92. 6
If bit 5 “internally calibrated” is set, the values are calibrated absolute measurements,
7
which should be interpreted according to the section “Internal Calibration” below. If bit 4 8
“externally calibrated” is set, the values are A/D counts, which are converted into real 9
units per the subsequent section titled “External Calibration”. 10
Measured parameters are reported in 16 bit data fields, i.e., two concatenated bytes. 11
To guarantee coherency of the diagnostic monitoring data, the host is required to 12
retrieve any multi-byte fields from the diagnostic monitoring data structure (IE: Rx Power 13
MSB - byte 104 in A2h, Rx Power LSB - byte 105 in A2h) by the use of a single two- 14
byte read sequence across the serial interface. 15
Measurements are calibrated over specified device operating temperature and voltage 16
and should be interpreted as defined below. Alarm and warning threshold values 17
should be interpreted in the same manner as real time 16 bit data. 18
Internal Calibration 19
1) Internally measured transceiver temperature. Represented as a 16 bit signed twos 20
complement value in increments of 1/256 degrees Celsius, yielding a total range of – 21
128°C to +128°C. Temperature measurement is valid from –40°C to +125°C with an 22
accuracy of ± 3°C. The temperature sensor is located in the center of the module 23
and is typically 5 to 10 degrees ho tter than the module case. See Tables 3.12 and 24
3.13 below for examples of temperature format. 25
2) Internally measured transceiver supply voltage. Represented as a 16 bit unsigned 26
integer with the voltage defined as the full 16 bit value (0 – 65535) with LSB equal to 27
100 µVolt, yielding a total range of 0 to +6.55 Volts. Accuracy is ±100mV. 28
3) Measured TX bias current in µA. Represented as a 16 bit unsigned integer with the 29
current defined as the full 16 bit value (0 – 65535) with LSB equal to 2 µA, yielding a 30
total range of 0 to 131 mA. Accuracy is ± 10%. Early versions of the digital 31
diagnostic standard (SFF-8472) used a scale factor of 1µA/AD Count for interpreting 32
laser bias current readings. SFF-8472 later changed the scale factor to the current 33
value of 2µA/AD Count. All Finisar modules using a scale factor of 2µA/AD Count 34
have an ASCII “A” written in byte 56 of the ‘vendor rev’ field (see table 3.1). Legacy 35
Finisar modules using a scale factor of 1µA/AD Count contain either zero or ASCII 36
space (20h) or one of two place holders: “X1—“, “1A—“, in location 56. 37
4) Measured TX output power in mW. Represented as a 16 bit unsigned integer with 38
the power defined as the full 16 bit value (0 – 65535) with LSB equal to 0.1 µW, 39
yielding a total range of 0 to 6.5535 mW (~ -40 to +8.2 dBm). Data is factory 40