Software UART for 89c51

[djc]

Hi,

I need two serial ports in my project. I want to use 89c51 controller, which has only one serial port. So i have some doubts regarding this as follows.

1) If we use software UART, then how many devices could be connected on single serial port.
2) Would we need max232 or 485 for software UART.
3) If i want to use RFID reader from which controller will only receive the signal and one wireless
module to which controller will only send the signal. SO can i connect RFID to Rx pin of controller
and wireless module to Tx pin of controller. Will it help or a chaos.
4) If i use CD4066, still will i need MAX232 or 485 to connect with controller's RX and TX.

Please Guide

Thanx in advance

 

[horace1]

Hi,

I need two serial ports in my project. I want to use 89c51 controller, which has only one serial port. So i have some doubts regarding this as follows.

1) If we use software UART, then how many devices could be connected on single serial port.
2) Would we need max232 or 485 for software UART.
3) If i want to use RFID reader from which controller will only receive the signal and one wireless
module to which controller will only send the signal. SO can i connect RFID to Rx pin of controller
and wireless module to Tx pin of controller. Will it help or a chaos.
4) If i use CD4066, still will i need MAX232 or 485 to connect with controller's RX and TX.

Please Guide

Thanx in advance

1. a Tx can transmit to as many receivers as it can drive - clearly you can only receive from one transmitter unless you use open collector bus or similar
2. if the receiver you are sending too needs RS232 you will need a MAX232
3. yes, you can transmit to one device and receive from another - you can have problems if they are different baud rates etc
4. what is the requirement of a CD4066? TTL or RS232

 

[djc]

CD4066 is a multiplexing IC. I haven't used it till now, but read that using it, we can interface two serial devices. I don't know how many. SO not sure about your question.

 

[andre_luis]

There are many variants of the 89C51 family which have 2 UARTs built inside. You can consider this option just performing few changes on program, mainly at some special function registers. Take a look on Silabs products.

 

[djc]

yes you are right andre....but i don't have a programmer which will support the controller with two serial port.Any other solution.

 

[andre_luis]

You can do it by a soft UART as you suggested, but sometimes have constraints to do that, because you need to dedicate resources for that, such as a timer to generate proper timings for the baud to TX, and reserve an input interrupt pin to detect incoming bits from RX

 

[djc]

Means normal GPIO pin for transmitting and interrupt for receiving. And use timer for generating specific baud rate. Two separate pins for two separate purpose, right.