Telit Wireless Solutions ME910G1, Руководство по конструкции

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ME910G1 Hardware Design Guide
1VV0301593 Rev.12
Page 48 of 93 2021-09-24
Not Subject to NDA
RS232 Level Translation
To interface the ME910G1 with a PC com port or an 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 0/1.8V 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
therefore some sort of level translation is always required.
The easiest way to translate levels and invert the signal is to use a single chip level
translator. There are a multitude of them, which differ in the number of drivers and
receivers 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 0-1.8V UART to
the RS232 level. The receiver is the translator from the RS232 level to 0-1.8V UART.
In order to translate the whole set of control lines of the UART you will need:
• 5 drivers
• 3 receivers
An example of RS232 level adaptation circuitry could be done using a MAXIM transceiver
(MAX218)
In this case the chipset is capable to translate directly from 1.8V to the RS232 levels
(Example done on 4 signals only).
Figure 14: example circuitry