User's Manual
Table Of Contents
- SB555 Hardware Integration
- Contact Information
- Table of Contents
- 1: About this Guide
- 2: Mechanical Integration
- 3: Electrical Integration
- 4: Serial Interfaces
- 5: Voice Interface
- 6: Control Signals
- 7: RF Integration
- Appendix A: Host Connector Pinouts
- Appendix B: Sample Integration
- Appendix C: Electrostatic Discharge
Serial Interfaces
Rev 1.0 Apr.02 Proprietary and Confidential 43
The SB555 is also protected by this FET when the
modem is powered down while the MCU
remains powered up. The modem’s input pins
should not have a voltage applied to them that is
more than 0.3 V above V
CC
, which could
otherwise happen when the modem is powered
down.
Pin 25: GND
This is a signal ground made available in
proximity to the other serial port pins for conve-
nience.
Pin 26: /DSR1
Data Set Ready is normally asserted following
successful completion of a modem’s self-test and
initialization. DSR is deasserted when the
modem is in shutdown state, to advise the host
that it is not available for use.
DSR is optional but recommended. If not used, it
can be left unconnected.
Pin 27: /RTS1
Request To Send is asserted by the host when it is
capable of receiving data from the modem, and
deasserted to prevent overflow.
The modem cannot ignore RTS, so if it is not
used, it must be tied active (low) by connecting to
ground; however doing this will risk data
overflow at the host device.