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AN-2030: Digital Diagnostic Monitoring Interface for Optical Transceivers F i n i s a r
9/26/02 Revision D Page 19
External Calibration 1
Measurements are raw A/D values and must be converted to real units using calibration 2
constants stored in EEPROM locations 56 – 95 at 2 wire serial bus address A2h (see 3
Table 3.15). Calibration is valid over specified device operating temperature and 4
voltage. Alarm and warning threshold values should be interpreted in the same manner 5
as real time 16 bit data. 6
1) Internally measured transceiver temperature. Module temperature, T, is given by the 7
following equation: T(C) = T
slope
* T
AD
(16 bit signed twos complement value) + T
offset
. 8
The result is in units of 1/256C, yielding a total range of –128C to +128C. See Table 9
3.15 for locations of T
SLOPE
and T
OFFSET
. Temperature measurement is valid from –10
40°C to +125°C with an accuracy of ± 3°C. The temperature sensor is located in the 11
center of the module and is typically 5 to 10 degrees hotter than the module case. See 12
Tables 3.12 and 3.13 above for examples of temperature format. 13
2) Internally measured transceiver supply voltage. Module internal supply voltage, V, is 14
given in microvolts by the following equation: V(µV) = V
SLOPE
* V
AD
(16 bit unsigned 15
integer)
+ V
OFFSET
. The result is in units of 100µV, yielding a total range of 0 – 6.55V. 16
See Table 3.15 for locations of V
SLOPE
and V
OFFSET
. Accuracy is ±100mV. 17
3) Measured transmitter laser bias current. Module laser bias current, I, is given by the 18
following equation: I(µA) = I
SLOPE
* I
AD
(16 bit unsigned integer) + I
OFFSET
. This result is 19
in units of 2 µA, yielding a total range of 0 to 131 mA. See Table 3.15 for locations of 20
I
SLOPE
and I
OFFSET
. Accuracy is ± 10%. Early versions of the digital diagnostic standard 21
(SFF-8472) used a scale factor of 1µA/AD Count for interpreting laser bias current 22
readings. SFF-8472 later changed the scale factor to the current value of 2µA/AD 23
Count. All Finisar modules using a scale factor of 2µA/AD Count have an ASCII “A” 24
written in byte 56 of the ‘vendor rev’ field (see table 3.1). Legacy Finisar modules using 25
a scale factor of 1µA/AD Count contain either zero or ASCII space (20h) or one of two 26
place holders: “X1—“, “1A—“, in location 56. 27
4) Measured coupled TX output power. Module transmitter coupled output power, 28
TX_PWR, is given in µW by the following equation: TX_PWR (µW) = TX_PWR
SLOPE
* 29
TX_PWR
AD
(16 bit unsigned integer)
+ TX_PWR
OFFSET
. This result is in units of 0.1µW 30
yielding a total range of 0 – 6.5mW. See Table 3.15 for locations of TX_PWR
SLOPE
and 31
TX_PWR
OFFSET
. Data is factory calibrated to absolute units using the most 32
representative fiber output type. Accuracy is ±3dB. Data is not valid when the 33
transmitter is disabled. 34
35