User's Guide

User’s Guide SB320 Product Description
2110059 Rev 1.1 Proprietary and Confidential Page 91
Modem Control Interface
Modem control is comprised of two inputs:
1. \SHDN: Graceful Shutdown
This is an active low input.
When activated this signal instructs the modem to de-register from the network, and
power down. When this activity is completed the \STATUS_OUT3 line is driven low
(on) indicating to the host that power may be safely removed from the device.
The purpose of this process is to prevent corruption of the data in non-volatile memory.
There is CDPD network housekeeping which goes on transparent to the user. Removing
power or resetting arbitrarily can corrupt this data. When the \SHDN signal is detected,
the modem will complete all housekeeping and send the de-register message to the
network before asserting \STATUS_OUT3.
Timing between the assertion of \SHDN and the reply on \STATUS_OUT3 can range
from a minimum of 20ms and a maximum of 2 seconds. The signal is polled at intervals
of 1 second. Aspects of network traffic at the time the signal is detected also determine
the timing for a giving situation.
The modem must be powered down or reset before it is again ready for use.
2. \RESET: Hardware Reset
This is a hardware reset of the modem. This input should be externally pulled high and
driven low for at least 100ms to reset.
Status Signal Interface
Status Outputs
There are three status outputs provided. These are active low and defined as follows:
1. \STATUS_OUT1: Power, RF Channel Status
• Permanently low (on) when power is on but no cellular channel is acquired. This
output is high (off) when the modem goes into CDPD sleep.
• Pulses low (on) once per second with 10% duty cycle (100ms on : 900ms off) if the
modem has acquired a cellular channel.
• Pulses low (on) twice per second with 10% duty cycle (100ms on : 100ms off :
100ms on : 700ms off) if modem is registered on a CDPD channel.
2. \STATUS_OUT2: Transmitter Key
• Low (on) when the transmitter is keyed.
3. \STATUS_OUT3: Power Down OK
• When low (on), this indicates it is safe to remove power to the modem or issue a
reset. This works in concert with the \SHDN signal noted above.
Status Inputs
There are four TTL-level status input lines provided. There are currently no features that use these
inputs. They are managed within the modem and may be left floating.