User's Manual

C1 March 2010
M7
RS-422 receivers have built-in bias resistors, offering the network a true
“1/8 unit load”. In most allocations, these internal bias resistors are sufficient,
and an external bias resistor is not required.
4.7. Low Power Mode (LPM)
The M
7 modem, has the ability to be put into a low power mode (LPM). In
LPM the modem draws much less current from the DC input. In LPM, the
internal radio in the M7 is disabled, as well as certain current-consuming
hardware circuits. The ability of the M7 to go into LPM is set with a
configuration bit, using the ATSM 1 command. ATSM 1 configures the M7 to
monitor the DTR input line, and enter the LPM mode whenever DTR is
negated. If the DTR signal is asserted, the M7 modem will operate normally.
The ATSM 2 command forces the M7 modem into the low-power mode. IN
the Low Power mode, the M7’s radio circuits are off, but it will still respond to
serial commands and it will still transmit characters over the air, albeit with
some latency as it has to power-up the radio each time it wishes to transmit.
The ATSM 0 command returns the M7 modem into the normal-operating
mode with the receiver and transmitter operational.
The M7 can switch between LPM and normal mode using the DTR line, and it
switches much faster than using the DC power supply. The M7 takes about
½ of a second to power on when DC is applied, but can switch between
normal and LPM in about 25milliseconds.
The factory default value for the ATSM setting is 0. When ATSM is a zero,
the M7 will not ever enter the LPM mode, and the DTR input signal is ignored.
DTR negated means it is a negative voltage. A voltage less than zero volts
applied to DTR will turn the M7 off by putting it into LPM.
To assert the DTR signal (turn the modem on), the DTR line must be high (>
3V). DTR is an input to an RS-232 transceiver IC. It is ESD protected, and
is safe for voltages from –20V to +20V input.