Rainbow Electronics DS3150 - Manual (Page 15)

DS3150
15 of 22
Table 2A. SIGNAL DESCRIPTIONS (continued)
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 (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: 6.81k
Ω ±2%
T3: 5.23k Ω ±2%
STS-1: 4.53k Ω ±2%
When switching among T3, E3, and STS-1 modes, do not allow OFSEL to float. Instead,
hardwire the highest resistor value and switch in series or parallel resistors as needed.
Example: For a T3/E3 application, hardwire 5.23kΩ for T3 and switch in series 1.58kΩ to
get 6.81kΩ for E3.
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 Three-state. This input determines whether the Tx+ and Tx- analog output
signals are forced into three-state or are active. This input also controls the jitter attenuator
(Table 2C).
0 = three-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
Ω coax line. They are coupled to the coax line through a 2:1 step-down
transformer (Section 1). These outputs can be three-stated through the TTS* input signal.
V
DD
-
Positive Supply. 3.3V
± 5%. All V
DD
signals should be tied together.
V
SS
-
Ground Reference. All V
SS
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:
1) I3 indicates an input capable of detecting three states: high, low, and float. All I3 inputs have an
internal 10kΩ pullup to 1.5V.
2) O3 indicates an output that is three-state capable.
3) Symbols appended with an asterisks (*) are active-low signals.