multiserial port connection

[engineer23]

Hi there,
can anyone help me? I want to connect two serial port to pic18f452 , I mean that i want to connect GSM modem and a digital camera (μCAM) and both of them need serial port but as you know that pic18 is able to connect with one serial port only!!

 

[bohumilfulin]

try to think
1. as second serial port use any pins and do it by FW. not so bad I have been using it up to 57600B
2. use HW separator like 4066, ... exists many ways how to do it.

 

[andre_luis]

I already used one UART of uC to receive 2 RX from external deveices, separated by 2 Diodes.
However there are some constraints :

>> Both devices must communicate at same Baud rate.
>> This topology works just for receiving data, not to transmit.
>> Firmware is responsible to identify incomming data and detect (CRC / Checksum) if were received simultaneously.

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[engineer23]

try to think
1. as second serial port use any pins and do it by FW. not so bad I have been using it up to 57600B
2. use HW separator like 4066, ... exists many ways how to do it.

would you explain more please?!:roll:
what do you mean by separator like 4066?

 

[alexxx]

what do you mean by separator like 4066?

Take a look at this link:
Three-state logic - Wikipedia, the free encyclopedia

Also I could suggest 74126, I have used it in the past for the same reason.

But anyway, if both devices are attempting to send at the same time and you have no control of it, then it is better to use an MCU with a second serial port. If you have control of the timing, then it is OK to go on with controled buffers, or diodes, or even simple resistors (but with a proper Ohm value).

 

[andre_luis]

would you explain more please?

You did not explained what C compiler are using.
However, some ones have ready-to-use APIs wich performs that feature and you can select even built-in UART module (hardware) or handshake I/O pins (firmware).

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[engineer23]

You did not explained what C compiler are using.
However, some ones have ready-to-use APIs wich performs that feature and you can select even built-in UART module (hardware) or handshake I/O pins (firmware).

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I am using MikroC compiler .. it seems the idea is not clear the camera and GSM will not operate together, the camera will first capture an image and transmit it to the PIC then the pic will send the image using the GSM modem to an external mobile device ... i thought of using a multiplexer at TX of PIC and demultiplexer at RX of the PIC with the control signal of each connected to a pin .. what do you guyz think ??

 

[andre_luis]

...the camera and GSM will not operate together... the camera will first capture an image and transmit it to the PIC...then the pic will send the image using the GSM modem to an external mobile device ...

The working you described means that is not necessary both devices communicate simultaneously to microcontroler.
Once this means a time multiplexing control, the switch sugested by bohumiffulin may fit what you need.

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