User's Manual
Table Of Contents
- GC864 Hardware User Guide
- APPLICABILITY TABLE
- 1. Introduction
- 2. Overview
- 3. GC864 Mechanical Dimensions
- 4. GC864-QUAD/PY Module Connections
- 5. Hardware Commands
- 6. Power Supply
- 7. Antenna
- 8. Logic Level Specifications
- 9. Serial Ports
- 10. Audio Section Overview
- 11. General Purpose I/O
- 11.1. GPIO Logic Levels
- 11.2. Using a GPIO Pad as INPUT
- 11.3. Using a GPIO Pad as OUTPUT
- 11.4. Using the RF Transmission Control GPIO4
- 11.5. Using the RFTXMON Output GPIO5
- 11.6. Using the Alarm Output GPIO6
- 11.7. Using the Buzzer Output GPIO7
- 11.8. Magnetic Buzzer Concepts
- 11.9. Using the Temperature Monitor Function
- 11.10. Indication of Network Service Availability
- 11.11. RTC Bypass Out
- 11.12. VAUX1 Power Output
- 12. DAC and ADC Section
- 13. Mounting the GC864-QUAD/PY on the Board
- 14. Packing System
- Conformity Assessment Issues
GC864 Hardware User Guide
1vv0300733 Rev.12 – 2009-06-04
9.2. RS232 Level Translation
In order to interface the Telit GC864-QUAD/PY with a PC com port or a RS232
(EIA/TIA-232) application a level translator is required. This level translator must
• invert the electrical signal in both directions
• change the level from 0/3V to +15/-15V
Actually, the RS232 UART 16450, 16550, 16650 & 16750 chipsets accept signals with
lower levels on the RS232 side (EIA/TIA-562), allowing for a lower voltage-multiplying
ratio on the level translator. Note that the negative signal voltage must be less than
0V and hence some sort of level translation is always required.
The simplest way to translate the levels and invert the signal is by using a single chip
level translator. There are a multitude of them, differing in the number of driver and
receiver and in the levels (be sure to get a true RS232 level translator not a RS485 or
other standards).
By convention the driver is the level translator from the 0-3V UART level to the RS232
level, while the receiver is the translator from RS232 level to 0-3V UART.
In order to translate the whole set of control lines of the UART you will need:
• 5 driver
• 3 receiver
NOTE:
The digital input lines working at 2.8VCMOS have an absolute maximum input voltage
of 3,75V; therefore the level translator IC shall not be powered by the +3.8V supply of
the module. Instead it shall be powered from a +2.8V / +3.0V (dedicated) power
supply.
This is because in this way the level translator IC outputs on the module side (i.e.
GC864-QUAD/PY inputs) will work at +3.8V interface levels, stressing the module
inputs at its maximum input voltage.
This can be acceptable for evaluation purposes, but not on production devices.
NOTE:
In order to be able to do in circuit reprogramming of the GC864-QUAD/PY firmware,
the serial port on the Telit GC864-QUAD/PY shall be available for translation into
RS232 and either it is controlling device shall be placed into tristate, disconnected or
as a gateway for the serial data when module reprogramming occurs.
Only RXD, TXD, GND and the On/off module turn on pad are required to the
reprogramming of the module, the other lines are unused.
All applicator shall include in their design such a way of reprogramming the GC864.
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