User's Manual

Interface specification: Interface to an RS-232 device 43
RIM 902M OEM Radio Modem – Integrator’s Guide
Shutdown will normally require several seconds to complete, and the radio
should not be disturbed while it is shutting down. Attempting to communicate
with the radio during shutdown may extend the time taken to perform
shutdown operations. The ONI signal will be de-asserted (low) when the radio
has shut down.
All serial inputs to the radio should be low when the radio is turned off. This
ensures that power consumption will be reduced to the lowest possible levels.
Note that if any line is left in the high state, as much as 5 mA may flow into the
radio modem.
MPAK data that has been received by the RIM 902M from the Mobitex
network, but which has not been transferred to the computing device, will not
be saved. The MPAKs will be lost when the unit enters shutdown or is turned
off.
A controlled shutdown is necessary to allow the RIM 902M to tell the Mobitex
network that it is off air.
Interface to an RS-232 device
The RIM 902M serial interface operates at 3.0V, making it compatible with
many existing system designs. In most cases, the RIM 902M can be connected
directly to a micro-controller without any additional interface logic. If the radio
modem is to be connected directly to a PC or other RS-232 device, an interface
must be provided.
Interface to microprocessor
The RIM 902M can be controlled by a wide variety of microcontrollers and
microprocessors, such as the Intel 8051 or 80386, or Motorola 68000.
A standard 8250 Universal Asynchronous Receiver/Transmitter (UART)
interface may be used as the means for communicating with the
microprocessor’s data bus.