HDMP-1512 (Tx), Signal Definitions
Symbol
Signal Name
I/O
Logic Type
Description
CAP0[A:B]
Loop Filter Capacitor
Pins [79,80]
C
PLL filter capacitor should be connected from pins
79 and 80 to pins 1 and 2 (typical value = 0.01 µF).
See Figures 18, 19, 20, and 21.
CAP1[A:B]
-COMGEN
-ECLKSEL
Loop Filter Capacitor
Pins [1,2]
C
PLL filter capacitor should be connected from pins
79 and 80 to pins 1 and 2 (typical value = 0.01 µF).
See Figures 18, 19, 20, and 21.
Comma Generate
Pin [32]
Input
Input
Input
TTL
TTL
An active low input, causes the transmitter to
internally generate the positive disparity K28.5 byte
(0011111010) for transmission.
External Clock Select
Pin [69]
An active low input, selects the TBC inputs to be used
as the serial clock, bypassing the PLL. Used mainly
for testing.
EWRAP
FAULT
Enable Wrap
Pin [71]
TTL
TTL
Works in conjunction with TS1 and TS2 to specify
input and output ports.
Laser Fault Indicator Output
Pin [29]
Indicates the laser output level has moved outside of
the window detector set boundary and the laser test
capacitor (LZTC) has discharged to a fault level. This
output is reset by the -LZON pin.
GND_A
Analog Ground
Pins [3,4]
S
S
Normally 0 volts. Used to provide a clean ground plane
for the critical PLL and high speed analog cells.
GND_LOG
Logic Ground
Pins [31,35,70,74]
Normally 0 volts. Used for all internal PECL logic.
Should be completely isolated from the noisy TTL
ground.
GND_LZ
Laser Ground
Pins [25,26]
S
S
Normally 0 volts. Used for all laser circuitry.
GND_LZHS Laser High Speed
Ground
Normally 0 volts.
Pins [10,18]
GND_TTL
± LOUT
LZBTP
TTL Ground
Pins [39,40,65,66]
S
Output
C
Normally 0 volts. Used for all TTL I/O buffer cells.
Local Serial Data
Pins [8,9]
BLL
High speed data port, typically connected to the ± LIN
port on the local receiver during serial wrap mode.
Laser Bandgap Test
Point
Pin [28]
This pin is internally set to 2.3 VDC and normally
should connect to one terminal of the laser DC bias
resistor (pot1 Figure 3).
LZCSE
Laser Current Source
Emitter
Pin [14]
C
Used to set the bias current of the AC laser driver.
Typical use is shown in Figure 3 where pot2 is used to
set the laser modulation depth.
LZDC
Laser DC Drive
Pin [21]
C
C
Used to control the laser diode DC bias (Figure 3).
± LZOUT
Laser Driver Serial
Output
AC driver to the laser diode. The outputs should be AC
coupled to the laser bias circuit.
Pins [19,20]
LZMDF
-LZON
Laser Monitor Diode
Feedback
Pin [22]
C
Connects to the laser monitor diode and one terminal of
the laser DC bias resistor (pot1). Under normal
operating conditions, the voltage on this pin will
be 1.85 V.
Laser Control and
Reset
Pin [30]
Input
TTL
The laser diode is turned on (active low) or off (high)
with this input. In the off state the capacitor on pin
LZTC charges, resetting the window
detector (Figure 3).
669
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