NCN5193
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7
Table 9. PIN DESCRIPTIONS
Symbol Pin Name Description
AREF Analog reference voltage Receiver Reference Voltage. See Table 2.
CDREF Carrier detect reference voltage Carrier Detect Reference voltage. The value should be 80 mV below AREF to set the
carrier detection to a nominal of 100 mV
p−p
.
RESETB Reset digital logic When at logic low (V
SS
) this input holds all the digital logic in reset. During normal
operation RESETB should be at V
DD
.
RTSB Request to send Active−low input selects the operation of the modulator. TxA is enabled when this
signal is low. This signal must be held high during power−up.
RxAP Analog filter amplifier positive
terminal
Positive terminal of the receive filter. For a reference implementation of the receive
filter see Figure 2
RxAN Analog filter amplifier positive
terminal
Negative terminal of the receive filter. For a reference implementation of the receive
filter see Figure 2
RxAFI Analog receive comparator input Positive input of the carrier detect comparator and the receiver filter comparator.
TxD Digital transmit input Input to the modulator accepts digital data in NRZ form. When TxD is low, the modu-
lator output frequency is 2200 Hz. When TxD is high, the modulator output frequency
is 1200 Hz.
XIN Oscillator input Input to the internal oscillator must be connected to a parallel mode ceramic resonator
when using the internal oscillator or grounded when using an external clock signal.
XOUT Oscillator output Output from the internal oscillator must be connected to an external clock signal or to
a parallel mode ceramic resonator when using the internal oscillator.
CLK1 Programmable Clock Output Output signal derived from oscillator output, frequency division set by internal register.
CLK2 Programmable Clock Output Output signal derived from oscillator output, frequency division set by internal register.
CBIAS Comparator bias current Connection to the external bias resistor. R
BIAS
should be selected such that AREF /
R
BIAS
= 10 mA ± 5%
CD Carrier detect output Output goes high when a valid input is recognized on RxA. If the received signal is
greater than the threshold specified on CDREF for four cycles of the RxA signal, the
valid input is recognized.
RxAF Analog receive filter output The output of the three pole high pass receive data filter
RxD Digital receive output Signal outputs the digital receive data. When the received signal (RxA) is 1200 Hz,
RxD outputs logic high. When the received signal (RxA) is 2200 Hz, RxD outputs logic
low. The HART receive data stream is only active if Carrier Detect (CD) is high.
MODE Digital input Selects the clock source. Connecting this pin to VDD disables the internal oscillator.
The chip then requires an external clock source. Connecting this pin to VSS enables
the internal oscillator to drive the external crystal or ceramic resonator
TxA Analog transmit output Transmit Data Modulator Output. A trapezoidal shaped waveform with a frequency of
1200 Hz or 2200 Hz corresponding to a data value of 1 or 0 respectively applied to
TxD. TxA is active when RTSB is low. TxA equals 0.5 V when RTSB is high.
SCLK SPI bus clock line Serial communication clock line
DATA SPI bus data line Serial communication data line.
CS SPI bus chip select Serial communication chip select line. Pulled high by microcontroller while a frame is
transmitted.
JUMP DAC Alarm value When a problem is detected, such as a clock failure or the watchdog going off, the DAC
will jump to VSS or DACREF, depending on whether this pin is connected to VSS or
VDD respectively.
DACREF DAC Reference This is the high value of the output and can be connected to any voltage between AREF
and VDD.
DAC DAC Output Output of a 17 bit Sigma−Delta Modulator
KICK Watchdog Kick Periodically a pulse should be provided to reset the watchdog. This can be configured in
internal registers for an internal 1.8kHz signal, or to an external signal provided to this pin.
VPOR POR Input Input to the POR comparator. The voltage on this pin is compared with AREF. An ex-
ternal resistor divider should divide the supply voltage to this pin.
VDD Digital power Power for the digital modem circuitry
VDDA Analog supply voltage Power for the analog modem circuitry
VSS Ground Digital ground
VSSA Analog ground Analog ground