DS3150
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SIGNAL DESCRIPTIONS Table 2A (cont.)
Signal
Name
I/O
Description
TDS1/
OFSEL
I
Transmit Data Select Bit 1 / Oscillator Frequency Select. If EFE = 1, this pin (TDS1)
and signals TDS0 and TESS select the source of the transmit data (see Table 2B). If
MCLK is tied low, TDS1 is internally pulled low and a resistor connected between
this pin (OFSEL) and ground determines the frequency of an internal oscillator. The
following resistor values should be used for specific applications.
E3:
6.81 k
±2%
T3:
5.23 k
±2%
STS1: 4.53 k
±2%
If EFE = 0, this signal is ignored.
TESS
I3
T3 / E3 / STS-1 Select. This input determines the mode of operation for the device.
0 = E3
1 = T3
Float = STS-1
TNEG
I
Transmit Negative Data. For bipolar data, the B3ZS/HDB3 encoder/decoder should
be disabled (ZCSE* = 1) and TNEG should be driven high to generate a negative
AMI pulse on the coax. For NRZ data, the B3ZS/HDB3 encoder/decoder should be
enabled (ZCSE* = 0), the NRZ data stream should be applied to TNRZ, and TNEG is
ignored and can be tied either high or low. TNEG is sampled either on the falling
edge of TCLK (ICE = 1 or Float) or the rising edge of TCLK (ICE = 0).
TPOS/
TNRZ
I
Transmit Positive Data. For bipolar data, the B3ZS/HDB3 encoder/decoder should
be disabled (ZCSE* = 1) and TPOS should be driven high to generate a positive AMI
pulse on the coax. For NRZ data, the B3ZS/HDB3 encoder/decoder should be
enabled (ZCSE* = 0), the NRZ data stream should be applied to TNRZ, and TNEG is
ignored and can be tied either high or low. TPOS/TNRZ is sampled either on the
falling edge of TCLK (ICE = 1 or Float) or the rising edge of TCLK (ICE = 0).
TTS*
I3
Transmit Tri-State. This input determines whether the TX+ and TX– analog output
signals are forced into tri-state or are active. This input also controls the jitter
attenuator. See Table 2C.
0 = tri-state the transmit output driver, disable TX jitter attenuation
1 = enable the transmit driver, disable TX jitter attenuation
Float = enable the transmit driver, enable TX jitter attenuation
TX+
TX–
O3
Transmit Analog Outputs. These differential AMI outputs drive the T3, STS-1, or E3
signal into the 75
coax line. They are coupled to the coax line via a 2:1 step-down
transformer. See Section 1 for details. These outputs can be tri-stated via the TTS*
input signal.
VDD
-
Positive Supply. 3.3V
± 5%. All VDD signals should be tied together.
VSS
-
Ground Reference. All VSS signals should be tied together.
ZCSE*
I
Zero Code Suppression Enable.
0 = B3ZS/HDB3 encoder/decoder enabled (NRZ interface enabled)
1 = B3ZS/HDB3 encoder/decoder disabled (NRZ interface disabled)
NOTES:
I3 indicates an input capable of detecting 3 states, high, low and float. All I3 inputs have an internal
10 k pull-up to 1.5V.
O3 indicates an output that is tri-state capable.
Symbols appended with an asterisks (*) are active low signals.