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HART Modem ASIC | HT1200M | Page
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8
Pin Description
IAREF: Analog Reference Voltage
This analog input sets the do operating point of the operational amplifiers and
comparators and is usually selected to split the do potential between VDD and Vss.
IAREF in DC Characteristics refer to Electrical Characteristics.
ICDREF: Carrier Detect Reference Voltage
This analog input controls at which level the carrier detect (OCD) becomes active.
This is determined by the do voltage difference between ICDREF and IAREF.
Selecting ICDREF-IAREF equal to 0.08 V
DC
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
Figure 3 Reset Timing
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
