u-blox SARA-R4 Series System Integration Manual

Contents

SARA-R4 series - System Integration ManualUBX-16029218 - R06 Design-inPage 64 of 1022.6 Data communication interfaces2.6.1 UART interface2.6.1.1 Guidelines for UART circuit designProviding the full RS-232 functionality (using the complete V.24 link)5If RS-232 compatible signal levels are needed, two different external voltage translators can be used to providefull RS-232 (9 lines) functionality: e.g. using the Texas Instruments SN74AVC8T245PW for the translation from1.8 V to 3.3 V, and the Maxim MAX3237E for the translation from 3.3 V to RS-232 compatible signal level.If a 1.8 V Application Processor (DTE) is used and complete RS-232 functionality is required, then the complete1.8 V UART interface of the module (DCE) should be connected to a 1.8 V DTE, as described in Figure 29.TxDApplication Processor(1.8V DTE)RxDRTSCTSDTRDSRRIDCDGNDSARA-R4(1.8V DCE)12 TXD9 DTR13 RXD10 RTS11 CTS6 DSR7 RI8 DCDGND0Ω TP0Ω TP0Ω TP0Ω TPFigure 29: UART interface application circuit with complete V.24 link in DTE/DCE serial communication (1.8V DTE)If a 3.0 V Application Processor (DTE) is used, then it is recommended to connect the 1.8 V UART interface of themodule (DCE) by means of appropriate unidirectional voltage translators using the module V_INT output as1.8 V supply for the voltage translators on the module side, as described in Figure 30.4 V_INTTxDApplication Processor(3.0V DTE)RxDRTSCTSDTRDSRRIDCDGNDSARA-R4(1.8V DCE)12 TXD9 DTR13 RXD10 RTS11 CTS6 DSR7 RI8 DCDGND1V8B1A1GNDU1B3A3VCCBVCCAUnidirectionalVoltage TranslatorC1 C23V0DIR3DIR2 OEDIR1VCCB2A2B4A4DIR41V8B1A1GNDU2B3A3VCCBVCCAUnidirectionalVoltage TranslatorC3 C43V0DIR1DIR3 OEB2A2B4A4DIR4DIR2TP0Ω TP0Ω TP0Ω TP0Ω TPFigure 30: UART interface application circuit with complete V.24 link in DTE/DCE serial communication (3.0 V DTE)Reference Description Part Number - ManufacturerC1, C2, C3, C4 100 nF Capacitor Ceramic X7R 0402 10% 16 V GRM155R61A104KA01 - MurataU1, U2 Unidirectional Voltage Translator SN74AVC4T7746 - Texas InstrumentsTable 24: Component for UART application circuit with complete V.24 link in DTE/DCE serial communication (3.0 V DTE)5 Flow control is not supported by “00”, “01” and “02” product versions, but the RTS input has to be set low to communicate over UART.The DTR input of the module has to be set low to have URCs presented over UART interface.6 Voltage translator providing partial power down feature so that the DTE 3.0 V supply can be also ramped up before V_INT 1.8 V supply