DDM پیرامیٹرز اور اکائیاں

ہماری ٹیم ترجمے پر کام کر رہی ہے۔ یہ مضمون عارضی طور پر اردو میں دستیاب نہیں ہے، اس لیے اسے انگریزی میں دکھایا جا رہا ہے۔

Digital diagnostics are five numbers a module measures about itself. Each is stored as a 16-bit value in module memory with a fixed unit, and the host converts it to °C, volts, milliamps or dBm. Knowing the raw encoding lets you read a dump by hand — and spot a module that reports nonsense.

The five monitors

Parameter	What it measures	Unit of the raw 16-bit value	Range
Temperature	module internal temperature	signed, 1/256 °C (high byte = whole degrees)	−128 … +128 °C
Supply voltage (Vcc)	3.3 V rail inside the module	unsigned, 100 µV	0 … 6.55 V
Tx bias current	laser drive current	unsigned, 2 µA	0 … 131 mA
Tx optical power	transmitted light power	unsigned, 0.1 µW	0 … 6.5535 mW
Rx optical power	received light power	unsigned, 0.1 µW	0 … 6.5535 mW

Optional extra monitors (laser temperature, TEC current) exist on some cooled/tunable modules.

Where they live — SFF-8472 (SFP class)

Real-time values are in the A2h block, bytes 96–105, two bytes each, MSB first:

Bytes	Monitor
96–97	Temperature
98–99	Vcc
100–101	Tx bias
102–103	Tx power
104–105	Rx power
106–109	optional (laser temp / TEC)

Whether DDM exists at all, and how it is calibrated, is declared in A0h byte 92 (Diagnostic Monitoring Type): bit 6 = DDM implemented, bit 5 = internally calibrated, bit 4 = externally calibrated, bit 3 = Rx power reported as average (1) or OMA (0). See Calibration.

For QSFP and CMIS modules the same units apply per lane — see Per-lane diagnostics.

Converting raw values

Temperature  °C  = signed16 / 256          0x1E80 = 7808   → 30.50 °C
Vcc          V   = uint16 × 0.0001         33000           → 3.300 V
Tx bias      mA  = uint16 × 0.002          3000            → 6.00 mA
Power        mW  = uint16 × 0.0001         8000            → 0.800 mW
Power        dBm = 10 · log10(mW)          0.800 mW        → −0.97 dBm

Handy anchors for optical power:

dBm	mW / µW	Raw (0.1 µW)
+3	2.0 mW	20 000
0	1.0 mW	10 000
−3	0.5 mW	5 000
−10	100 µW	1 000
−20	10 µW	100
−30	1 µW	10
−40	0.1 µW	1 (resolution floor)

Because the raw unit is 0.1 µW, DDM cannot resolve anything below −40 dBm; a reading of exactly −40 dBm (raw 0 or 1) means "no light", not a precise measurement. More dB arithmetic and rate/baud tables: Units & conversions.

What each parameter tells you

Temperature — rises with ambient and with port density; a module running hot ages its laser faster. Typical operating range 0…70 °C (commercial) or −40…85 °C (industrial).
Vcc — should sit near 3.3 V; a low or noisy reading points to the host slot, not the module.
Tx bias — the single best ageing indicator: the module raises bias to keep Tx power constant as the laser wears. Trend it (Failures).
Tx power — useful when measured; on inexpensive modules it may be a constant written to memory (DDM levels).
Rx power — the health of the far end and the fibre: compare against the receiver's sensitivity and against the installation baseline.

In CodingBox

The DDM screen performs these conversions live and plots the values with the module's own thresholds; the EEPROM editor shows the raw bytes 96–105 and byte 92 for verification.

Monitor byte positions and formats per specification: SFF-8472 A2h map (96–109), SFF-8636 lower page (22–57), CMIS lower page (14–25) and page 11h (154–201).

اگر آپ کو اس مضمون میں کوئی غیر درست بات یا غلطی نظر آئے تو متعلقہ حصہ منتخب کریں اور Ctrl+Enter دبا کر ۔