DS1864 datasheet(22/72 Pages) DALLAS

22 / 72 page

SFP Laser Controller and

Diagnostic IC

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Table 04h (Table 01h in DS1859 configuration) is the

location of the LTXP programmable threshold. Register

DDh of Table 04h (Table 01h in DS1859 configuration)

is the location of the LOS programmable threshold.

Alarms and Warnings

There are ten comparators for alarms and ten compara-

tors for warnings for the five analog channels: VCC,

Temperature, MON1, MON2, and MON3. These com-

parators have high and low threshold limits, which are

used to determine when alarm and warning flags are

triggered. A high alarm flag occurs when a comparator

determines if the monitored analog value is above a

programmable threshold. A low alarm flag occurs when

a comparator determines if the monitored analog value

is below a programmable threshold. The same applies

for high and low warning flags, though warning flags

are typically set to trip prior to the alarm flags. The pro-

grammable thresholds have a 2-byte set point in the

same format as the ADC values stored in Lower

Memory bytes 60h through 69h. The programmable

high and low thresholds for both alarms and warnings

are located in Lower Memory bytes 00h through 27h.

The status bits for the alarm flags are located in Lower

Memory bytes 70h and 71h. The status bits for the

warning flags are located in Lower Memory bytes 74h

and 75h. A high alarm or warning flag is set to a 1 when

the corresponding digital value exceeds the user pro-

grammed high threshold. A low alarm or warning flag

is set to a 1 when the corresponding digital value

goes below the user-programmed low threshold.

Comparisons of all measured values with high and low

alarm and warning limits are done automatically.

The MASK bits control which flags can assert the mask-

able interrupt bit, MINT (bit 0, address 71h of the Lower

Memory). The MASK bits are located in Table 01h,

bytes F8h through FBh, or Table 05h, bytes F8h

through FBh, depending on the state of the MASK bit

(Table 04h (Table 01h in DS1859 configuration), byte

DAh, bit 0). If the MASK bit is 0, then the values in

addresses F8h through FBh in Table 05h will determine

which flags will assert MINT. If the MASK bit is 1, then

the values in addresses F8h through FBh in Table 01h

(Table 00h in DS1859 configuration) will determine

which flags will assert MINT.

TX-F, INTX-F, and TX-D

The TX-F pin is used to indicate a DAC shutdown and/or

laser fault. See the logic diagram in Figure 12. The

TXDC control bit (bit 6, byte 6Eh of the Lower Memory)

is a software-controllable shutdown feature. It not only

triggers TX-F to go active when set to a 1, but will also

disable the DACs, shutting down the laser. The TX-D pin

acts like a hardware version of the TXDC bit, triggering

the TX-F pin and disabling the DACs when set high. The

MINT interrupt bit discussed earlier also can trigger the

TX-F pin if configured to enable when one of its alarm or

warning flags goes high. Four fast-trip flags also can

trigger TX-F to go active. The INTX-F pin, used for trig-

gering from an externally generated transmit fault sig-

nal, can also be used to trigger the TX-F pin. The INV bit

(bit 2, byte 89h, Table 04h (Table 01h in DS1859 config-

uration)) is used to invert the polarity of the TX-F pin.

TXF bit (bit 2, byte 6Eh, Lower Memory) is a status bit

that indicates the state of the output pin TX-F. The TX-F

pin is not latched, except in the case of a shutdown

fault. The status of TX-F will reset to inactive upon

removal of the causes of the alarms, or upon resetting of

the shutdown fault. The TX-F pin is open drain.

RX-LOS and INLOS

The RX-LOS pin is used to indicate a loss of received

signal on the MON3 (Received Power) input. RX-LOS

can be triggered by either the external signal, INLOS,

or the internal alarm, LOS flag. INLOS is an input pin

that can be used to indicate a loss of signal generated

from an external source. LOS flag (bit 2, byte 73h of

Lower Memory) can also be used to indicate a loss of

signal. LOS flag is active high when the value of MON3

goes below its threshold, set by programming byte

DDh of Table 04h (Table 01h in DS1859 configuration)

to the desired limit. To configure which signal triggers

RX-LOS, the LOSC bit (bit 6, byte 89h, Table 04h

(Table 01h in DS1859 configuration)) is used. If LOSC

= 1, INLOS is used to trigger the RX-LOS indicator. If

LOSC = 0, then the LOSC flag is used. The final control

bit for this logic is the INVL bit. The INVL bit (bit 0, byte

89h, Table 04h (Table 01h in DS1859 configuration)) is

used to invert the polarity of the RX-LOS pin. The RX-

LOS pin is open drain. See Figure 13 for details.

FETG Laser Safety Features

An auxiliary shutdown signal FETG can be asserted

during a safety fault to disconnect the laser from its

supply as a laser safety disconnect. The polarity of this

signal is determined by the FPOL bit (bit 7, byte DAh in

Table 04h (Table 01h in DS1859 configuration)). If

FPOL is 1, then FETG is high in a shutdown condition. If

FPOL is 0, then FETG is low in a shutdown condition.

A safety fault is a latched event that is generated from

the fast-trip flags (LTXP, HBAL, and HTXP). These flags

can be independently configured to initiate a safety

fault using the enable bits (bits 4, 5, and 6 in byte DAh

of Table 04h (Table 01h in DS1859 configuration)). A 1

for these bits enables that specific flag to generate a

safety fault, while a 0 masks the flag. When a safety

fault is generated, the DACs are disabled (forced to a

high-impedance state), FETG is disabled (driven low),

DS1864 Datasheet(PDF) 22 Page - Dallas Semiconductor

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