how make 2 source to connect PIC18F452 with rs232 ?

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asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia

Use the hardware UART for the high speed port and a software UART for the low speed port.
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SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

If the two sources are never active at the same time you can use a NAND gate to combine them into one UART. Put the NAND gate on the TTL line
between the RS232 level shifter and the PIC.

If you do use the hardware UART for the high speed port and a software UART for the low speed port then the processor will be busy the whole time the low speed port is recieving. That may cause the hardware UART buffer to overflow. If you reverse them the CPU won't be busy for so long.
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asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia