Telit Wireless Solutions UC864 manual RS232 level translation

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UC864-E Hardware User Guide

1vv0300766a Rev.1 - 31/01/08

8.2RS232 level translation

In order to interface the Telit UC864-E with a PC com port or a RS232 (EIA/TIA-232) application a level translator is required. This level translator must

ƒInvert the electrical signal in both directions

ƒTranslate the level from 0/2.6V 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 0-2.6V UART level to the RS232 level, while the receiver is the translator from RS232 level to 0-2.6V UART.

In order to translate the whole set of control lines of the UART you will need:

•5 drivers

•3 receivers

NOTE: The digital input lines working at 2.6V CMOS have an absolute maximum input voltage of 3.0V; therefore the level translator IC shall not be powered by the +3.8V supply of the module. Instead it shall be powered from a +2.6V / +2.9 (dedicated) power supply.

This is because in this way the level translator IC outputs on the module side (i.e. UC864-E inputs) will work at +3.8V interface levels, stressing the module inputs at its maximum input voltage.

NOTE: In order to be able to do in circuit reprogramming of the UC864-E firmware, the serial port on the Telit UC864-E shall be available for translation into RS232 and either it's 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 UC864-E.

Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved

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Contents UC864 Hardware User Guide UC864-E Hardware User Guide This document is relating to the following productsContents 10.3 10.411.1 11.2Disclaimer Overview Mechanical Dimensions Length 36.2 mm Width 30 mm Thickness 8mmUC864-E module connections PIN-OUTCmos Reserved 1 UC864-E Antenna connector Pin Signal FunctionHardware Commands Turning on the UC864-E10k Turning OFF the UC864-E Hardware shutdownHardware Unconditional Restart 10k +1.8 Power Supply Power Supply RequirementsUC864-E Hardware User Guide General Design Rules Electrical Design Guidelines1.2 + 12V input Source Power Supply Design Guidelines UC864-E Hardware User Guide Battery Source Power Supply Design Guidelines UC864-E Hardware User Guide Thermal Design Guidelines Power Supply PCB layout Guidelines Antenna Antenna RequirementsAntenna Installation Guidelines Logic level specifications Absolute Maximum Ratings -Not FunctionalOperating Range Interface levels Operating Range Interface levels 1.8V CmosReset signal Serial Ports Absolute Maximum Ratings Not FunctionalSignals of the UC864-E serial port are RS232 level translation UC864-E Hardware User Guide UC864-E Hardware User Guide 5V Uart level translation UC864-E Hardware User Guide USB Port Communication ports combinationsAudio Section Overview GeneralityDefinitions SelectionElectrical Characteristics Input lines microphoneOutput lines speaker EarMT BuffersGeneral Purpose I/O NotLogic level specifications Using the Alarm Output GPIO6 Using a Gpio Pad as InputUsing a Gpio Pad as Output Using the Buzzer Output GPIO7 Indication of network service availability LED status Device StatusRTC Bypass out VAUX1 power outputOperating Range VAUX1 power supply Mounting UC864-E on your board Debug of the UC864-E in production USB Vbus UsbidConformity Assessment Issues Safety Recommandations Document Change Log Revision Date Changes
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