A5191HRT AMIS HART™ Modem
3.0 Pin Descriptions
Table 3: Pin Descriptions
Symbol
IAREF
Pin Name
Analog Reference Voltage
Data Sheet
Description
Analog input sets the dc operating point of the operational amplifiers and comparators and is usually selected to split the
dc potential between V
DD
and V
SS
. See IAREF in DC Characteristics, Table 6
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 V
DC
will set the carrier detect to a nominal
100 mV
p-p
When at logic low (V
SS
) this input holds all the digital logic in reset. During normal operation INRESET should be at V
DD
.
INRESET should be held low for a minimum of 10nS after V
DD
= 2.5V as shown in Figure 3
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
Input accepts the 1200/2200Hz signals from the external filter
Positive input of the carrier detect comparator and the receiver filter comparator
Input to the modulator accepts digital data in NRZ form. When ITXD is low, the modulator output frequency is 2200Hz.
When ITXD is high, the modulator output frequency is 1200Hz.
Input to the internal oscillator must be connected to a parallel mode 460.8kHz ceramic resonator when using the internal
oscillator or grounded when using an external 460.8kHz clock signal
The current through this output controls the operating parameters of the internal operational amplifiers and
comparators. For normal operation, OCBIAS current is set to 2.54A.
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.
Signal is the square wave output of the receiver high-pass filter
Signal outputs the digital receive data. When the received signal (IRXA) is 1200Hz, ORXD outputs logic high. When the
received signal (IRXA) is 2200Hz, ORXD outputs logic low. ORXD is qualified internally with OCD.
Output provides the trapezoidal signal controlled by ITXD. When ITXD is low, the output frequency is 2200Hz. When
ITXD is high, the output frequency is 1200Hz. This output is active when INRTS is low and 0.5 V
DC
when INRTS is high.
Output from the internal oscillator must be connected to an external 460.8kHz clock signal or to a parallel mode
460.8kHz ceramic resonator when using the internal oscillator
Factory test pins; for normal operation, tie these signals as per Table 1 and Table 2
Power for the digital modem circuitry
Power for the analog modem circuitry
Analog and digital ground
ICDREF
Carrier Detect Reference Voltage
INRESET
INRTS
IRXA
IRXAC
ITXD
IXTL
OCBIAS
OCD
ORXAF
ORXD
OTXA
OXTL
Reset Digital Logic
Request to Send
Analog Receive Input
Analog Receive Comparator Input
Digital Transmit Input (CMOS)
Oscillator Input
Comparator Bias Current
Carrier Detect Output
Analog Receive Filter Output
Digital Receive Output (CMOS)
Analog Transmit Output
Oscillator Output
TEST(12:1) Factory Test
VDD
VDDA
VSS
VSSA
Digital Power
Analog Supply Voltage
Ground
Analog Ground
Figure 3: Reset Timing
Note:
This signal is also present on the LSI 20C15. It is labeled as Test6. The 20C15 data sheet mentions the reset function of this pin but does not emphasize its use to reset the chip. Reliable operation
of the modem requires a hardware reset as shown in Figure 3. This is true for the AMIS 12197-503 and 12197-504 as well as the LSI 20C15.
AMI Semiconductor - Rev. 2.0, Mar. 05
3
AMI [ AMI SEMICONDUCTOR ]
