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ST7537HS1
HOME AUTOMATION MODEM
ST7537HS1HOME AUTOMATION MODEM
June 1995
PIN CONNECTIONS HALF DUPLEX ASYNCHRONOUS 2400bps
FSK MODEM. Tx CARRIER FREQUENCY SYNTHESIZED
FROM EXTERNAL CRYSTAL. LOW DISTORTION Tx SIGNAL. Rx SENSITIVITY BETTER THAN 1mVRMS. CARRIER DETECTION. WATCH-DOG INPUT. RESET AND MASTER CLOCK OUTPUTS
FOR MICROCONTROLLER. POWER AMPLIFIER BIAS CURRENT CON-
TROL (HIGH IMPEDANCE IN Rx MODE). SIMPLE AND ECONOMICAL APPLICATION
SCHEMATICS. COMPATIBLE WITH CENELEC EN 50065-1
AND FCC SPECIFICATION. CARRIER DETECT CLAMPING ON RxD
PROGRAMMABLE (ALLOWING DEMODULA-
TION ON VERY LOW RECEIVE LEVEL,
1mVRMS TYPICALLY)
DESCRIPTIONThe ST7537HS1 is a half duplex asynchronous
FSK MODEM designed for home automation com-
munication on the domestic electric mains which
complies with the EN 50065-1 CENELEC stand-
ard.
It mainly operates from a 10V power supply and a
5V power supply for the microcontroller digital in-
terface.
It is interfaced to the power line by an external
driver, and a transformer (see Application Sche-
matic Diagram). Its data transmission rate is
2400 bps and its carrier frequency is 132.45kHz.
1/9
PIN DESCRIPTION
ST7537HS12/9
BLOCK DIAGRAM
TRANSMIT SECTIONThe transmit mode is set when Rx/Tx = 0, if Rx/Tx
is held at 0 longer than 1 second, then the device
switches automatically in the Rx mode. A new
activation of the Tx mode requires Rx/Tx to be
returned to 1 for a minimum 2 microsecond period
before being set to 0.
The Transmit Data (TxD) enter asynchronously the
FSK modulator with a nominal intra-message data
rate of 2400 bps.
The basic transmit frequencies are : f(TxD=0) = 133.05kHz f(TxD=1) = 131.85kHz
These frequencies are synthesized from a
11.0592MHz crystal oscillator; their precision is the
same as the crystal one’s (100ppm).
The modulated signal coming out of the FSK modu-
lator is filtered by a switched-capacitor band-pass
filter (Tx band-pass) in order to limit the output
spectrum and to reduce the level of harmonic com-
ponents.
The final stage of the Tx path consists of an opera-
tional amplifier which needs a feed-back signal
(PAFB) from the power amplifier as shown on
Application Schematic Diagram.
In Tx mode the Receive Data (RxD) signal is set to 1.
RECEIVE SECTION The receive section is active when Rx/Tx = 1.
The Rx signal is applied on RAI and filtered by a
band-pass switched capacitor filter (Rx band-pass)
centered on the carrier frequency and whose band-
width is around 12kHz.
The Rx filter output is amplified by a 20dB gain
stage which provides symetrical limitations for
large voltage. The resulting signal is down-con-
verted by a mixer which receives a local oscillator
synthesized by the FSK modulator block. Finally an
intermediate frequency band-pass filter (IF band-
pass) whose central frequency is 5.4kHz improves
the signal to noise ratio before entering the FSK
demodulator.
The coupling of the intermediate frequency filter
output (IFO) to the FSK demodulator input (DEMI)
is made by an external capacitor C5 (100nF ±10%,
10V) which cancels the Rx path offset voltage.
The RxD output delivers the demodulated signal if
the carrier detect (CD) signal is low and is set to
high level when CD = 1.
The RxD output can delivers the demodulated
signal whatever the level of CD (0 or 1) if Rx/Tx = 1
and TxD = 0 (see Figure 1).
ST7537HS13/9
ADDITIONAL DIGITAL AND ANALOG FUNC-
TIONS
Time baseA time base section delivers all the internal clocks
from a crystal oscillator (11.0592MHz). The crystal
is connected between XTAL1 and XTAL2 pins and
needs two external capacitors C3 and C4 (22pF
±10%, 10V) for proper operation.
Reset and watch-dogThe reset output (RSTO) is driven high when the
supply voltage is lower than Vrh (typically 7.6V) with
an hysteresis Vrh-Vrl (typically 300mV) or when no
negative transition occurs on the watch-dog input
(WD) for more than 1.5 second (see the timing
chart on Figure 2). When a reset occurs RSTO is
held high for at least 50ms.
Signal detectionThe Carrier Detect output (CD) is driven low when
the input signal amplitude on RAI is greater than
VCD for at least TCD (typically 6ms see the timing
chart on Figure 3). When the input signal desap-
pears or becomes lower than VCD, CD is held low
for at least Tcd before returning to a high level. VCD
is the carrier detection threshold voltage which is
set internally to detect 5mVRMS typically.
External power amplifier bias controlTwo dedicated digital output (PABC and PABC)
delivering a signal between 0V and 10V are driven
low respectively high, when the circuit is set in the
receive mode (Rx/Tx=1) or when the transmit mode
time out (1 second) is exceeded; in the same time
the output ATO is put in a high impedance state.
TESTING FEATURES An additionnal amplifier allows the observation of
the Rx band-pass filter output on pin RxFO. A direct input to the Tx band-pass filter and to the
IF filter (TxIFI) is selected when TEST3 = 1. The 1 second normal duration of the Tx to Rx
mode automatic switching is reduced to 488μs
and the 1.5 second watch-dog time out is reduced
to 46.3μs when TEST2 = 1. When TEST1 = 1 the Tx to Rx mode automatic
switching is desactivated and the functional mode
of the circuit is fully controlled by Rx/Tx. TEST4 is a reset input which allows an undelayed
control of RSTO and of the internal state of the
circuit.
POWER SUPPLIES WIRING PRECAUTIONSThe ST7537HS1 has two positive power supply
terminals (AVDD,DVDD) and two ground terminals
(AVSS,DVSS) in order to separate internal analog
and digital supplies. The analog and digital termi-
nals of each supply pair must be connected to-
gether externally for proper operation.
The VDD must be protected against short-circuit for
proper operation.
Figure 1 : Data Timing Chart
ST7537HS14/9
ABSOLUTE MAXIMUM RATINGS
GENERAL ELECTRICAL CHARACTERISTICS(A/DVDD = 10V, A/DVSS = 0V, DVCC = 5V and 0o C ≤ Tamb ≤ 70o C, unless otherwise specificied)
TRANSMITTER ELECTRICAL CHARACTERISTICS(A/DVDD = 10V, A/DVSS = 0V, DVCC = 5V and 0o C ≤ Tamb ≤ 70o C, unless otherwise specificied)
ST7537HS15/9
RECEIVER ELECTRICAL CHARACTERISTICS(A/DVDD = 10V, A/DVSS = 0V, DVCC = 5V and 0o C ≤ Tamb ≤ 70o C, unless otherwise specificied)
ADDITIONAL DIGITAL AND ANALOG FUNCTIONS ELECTRICAL CHARACTERISTICS(A/DVDD = 10V, A/DVSS = 0V, DVCC = 5V and 0o C ≤ Tamb ≤ 70o C, unless otherwise specificied)
Figure 2 : Reset and Watch-dog Timing Chart
Figure 3 : Carrier Detection Timing Chart
ST7537HS16/9
