TDK 73M2901/5V manual Hardware Description

73M2901/5V Advanced Single Chip Modem

HARDWARE DESCRIPTION

The 73M2901/5V is designed for a single +5 volt supply with low power consumption (~250mW @ 5 volts). The modem supports automatic standby idle mode. The modem will also accept a request to power down from the DTE via hardware control. No additional major components are required to complete the modem core logic. The modem provides direct firmware LED support via port pins.

The hybrid configuration is controlled by the state of the HBDEN pin. For driving a line-coupling transformer, HBDEN should be pulled high. For driving an external hybrid (load on TXAP and TXAN is 50kΩ or larger), HBDEN should be pulled low.

The 73M2901/5V provides firmware control for a hook relay driver (RELAY) as well as interrupt support for a ring detect opto-coupler (RING).

INTERRUPT PINS

HARDWARE FEATURES

∙Fully self-contained. “AT” Command interpreter and data pump

∙User pin available

∙Synchronous serial data I/O available

∙Asynchronous serial port

∙On-chip hybrid driver.

∙Autobaud capability from 300bps to 9600bps

POWER SUPPLY

Power is supplied to the 73M2901/5V via the VPD and VPA pins. The 73M2901/5V is designed for a single +5 (+/-10%) volt supply and for low power consumption (~250mW @ 5 volts). Ground Reference is provided at the VND and VNA pins.

LOW POWER MODE

The TDK 73M2901/5V supports a low power mode. If the low power standby option is enabled the 73M2901/5V will go into a power saving mode when idle. The oscillator will be running, clocks will be supplied to the UART, timers and interrupt blocks; but no clocks will be supplied to the CPU. Instruction processing and activity on the internal busses is halted. Normal operation is resumed when an interruption such as DTR, RING or ASRCH (any character send to the 73M2901/5V) is requested or when a reset occurs.

ANALOG LINE / HYBRID INTERFACE

The 73M2901/5V provides a differential analog output (TXAP and TXAN) and a single-ended analog input (RXA) with internal A/D and D/A converters. A driver is provided for an internal hybrid function.

The internal hybrid driver is capable of driving an external load matching impedance and a line- coupling transformer. If an external hybrid is to be used, the on-chip hybrid drivers can be reconfigured to drive a minimum load of 50kΩ and thus reduce the driver’s power consumption.

The external interrupt sources, DTR, ASRCH and RING, come from dedicated input pins of the same name.

DTR informs the 73M2901/5V that the host has requested the 73M2901/5V perform a specific function. The actual particulars of that function can be changed by “AT” commands (described in full in the TDK 73M2901 User’s Guide).

ASRCH informs the 73M2901/5V that the host is passing data to the 73M2901/5V over the DTE interface. This instructs the 73M2901/5V to begin looking for valid “AT” commands. This pin needs to be connected to the TXD pin.

RING informs the 73M2901/5V that the external DAA circuitry has detected a ring signal.

CRYSTAL OSCILATOR

The TDK 73M2901/5V single chip modem can use an external 11.0592 MHz reference clock or can generate such a clock using only a crystal and two capacitors. If an external clock is used, it should be applied to OSCIN.

SPECIFYING A CRYSTAL

The manufacturer of a crystal resonator verifies its frequency of oscillation in a test set-up, but to ensure that the same frequency is obtained in the application, the circuit conditions must be the same. The TDK 73M2901/5V modem requires a parallel mode (antiresonant) crystal, the important specifications of which are as follows:

Mode:	Parallel (antiresonant)
Frequency:	11.0592 MHz
Frequency tolerance:	±50	ppm	at	initial
	temperature.
Temperature drift:	±50 ppm additional over full
	Range.
Load capacitance:	18pF or 20pF
ESR:	75Ω max.
Drive level:	Less than 1mW.

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