The HT2015 is a single-chip, CMOS modem for use in Highway Addressable Remote Transducer (HART) field instruments and masters.
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MODEM HART HT2015
Hart Modem HT2015 Datasheet.
General Description The HT2015 is a single-chip, CMOS modem for use in Highway Addressable Remote Transducer (HART) field instruments and masters. The modem and a few external passive components provide all of the functions needed to satisfy HART physical layer requirements including modulation, demodulation, receive filtering, carrier detect and transmit-signal shaping. The HT2015 is pin-compatible with the SYM20C15. See the Pin Description and Functional Description sections for details on pin compatibility with the SYM20C15. The HT2015 uses Phase Continuous Frequency Shift Keying (FSK) at 1200 bits per second. To conserve power the receive circuits are disabled during transmit operations and vice versa. This provides the half-duplex operation used in HART communications.
Can be used in designs presently using the SYM20C15 or equivalent type chip
Single-chip, half-duplex 1200 bits per second FSK modem
Bell 202 shift frequencies of 1200 Hz and 2200 Hz
2.7V-5.0V power supply
Transmit-signal wave shaping
Receive band-pass filter
Low power: optimal for intrinsically safe applications
Internal oscillator requires 460.8 kHz crystal or ceramic resonator
Meets HART physical layer requirements
Industrial temperature range of -40 °C to +85 °C
Available in a 28-pin PLCC and 32-pin LQFP packages (LQFP pictured)
IAREF: Analog Reference Voltage This analog input sets the dc operating point of the operational amplifiers and comparators and is usually selected to split the dc potential between VDD and VSS. See IAREF in DC Characteristics on page 11.
ICDREF: Carrier Detect Reference Voltage This analog input controls at which level the carrier detect (OCD) becomes active. This is determined by the dc voltage difference between ICDREF and IAREF. Selecting ICDREF - IAREF equal to 0.08 VDC will set the carrier detect to a nominal 100 mVp-p.
INRESET: Reset Digital Logic When at logic low (VSS) this input holds all the digital logic in Reset. During normal operation INRESET should be at VDD. INRESET should be held low for a minimum of 10 nS after VDD = 2.5 V as shown in Figure 3.
INRTS: Request To Send This active-low input selects the operation of the modulator. OTXA is enabled when this signal is low. This signal must be held high during power-up.
IRXA*: Analog Receive Input This input accepts the 1200/2200 Hz signals from the external filter.
IRXAC: Analog Receive Comparator Input This is the positive input of the carrier detect comparator and the receiver filter comparator.
ITXD: Digital Transmit Input (CMOS) This input to the modulator accepts digital data in NRZ form. When ITXD is low, the modulator output frequency is 2200 Hz. When ITXD is high, the modulator output frequency is 1200 Hz.
IXTL: Oscillator Input This input to the internal oscillator must be connected to a parallel mode 460.8 kHz ceramic resonator when using the internal oscillator or grounded when using an external 460.8 kHz clock signal.
OCBIAS: Comparator Bias Current The current through this output controls the operating parameters of the internal operational amplifiers and comparators. For normal operation, OCBIAS current is set to 2.5 4A.
OCD: Carrier Detect Output This output goes high when a valid input is recognized on IRXA. If the received signal is greater than the threshold specified on ICDREF for four cycles of the IRXA signal, the valid input is recognized.
ORXAF*: Analog Receive Filter Output This signal is the square wave output of the receiver high-pass filter.
ORXD: Digital Receive Output (CMOS) This signal outputs the digital receive data. When the received signal (IRXA) is 1200 Hz, ORXD outputs logic high. When the received signal (IRXA) is 2200 Hz, ORXD outputs logic low. ORXD is qualified internally with OCD and is logic high when OCD is low.
OTXA: Analog Transmit Output This output provides the trapezoidal signal controlled by ITXD. When ITXD is low, the output frequency is 2200 Hz. When ITXD is high, the output frequency is 1200 Hz. This output is active when INRTS is low and 0.5 VDC when INRTS is high.
OXTL: Oscillator Output This output from the internal oscillator must be connected to an external 460.8 kHz clock signal or to a parallel mode 460.8 kHz ceramic resonator when using the internal oscillator.
TEST(12:1): Factory Test These are factory test pins. For normal operation, tie these signals as per Table 1.
VDD: Digital Power This is the power for the digital modem circuitry.
VDDA: Analog Supply Voltage This is the power for the analog modem circuitry.
VSS: Ground This is ground.
VSSA: Analog Ground This is the analog ground.
The HT2015 is a functional equivalent of the SYM20C15 HART Modem. It contains a transmit data modulator and signal shaper, carrier detect circuitry, analog receiver and demodulator circuitry and an oscillator.
The internal HART modem modulates the transmit-signal and demodulates the receive signal. The transmit-signal shaper enables the HT2015 to transmit a HART compliant signal. The carrier is detected by comparing the receiver filter output with the difference between two external voltage references. The analog receive circuitry band-pass filters the received signal for input to the modem and the carrier detect circuitry. The oscillator provides the modem with a stable time base using either a simple external resonator or an external clock source.