looking for solutions/ideas/chip for my project

John Doe1 · ‎2018-05-31

Posted on May 31, 2018 at 17:13

Hi,

As a beginner I develop projects on STM32 boards. It's a very good choice for me and I am glad that I chose STM32.

I create my small home project and I have a trouble to choose the appropriate additional solutions (stm32 also welcome as well).

Short description of the project:

I have master board and slave boards. Each slave boards in connected to master via rs485. Slave board accepts 3072 bytes (50 updates per second).

Each slave board is connected to master via independent uart.

The problem is that I can control only 6 independent uarts. I would like to control i.e. ~50 slaves by rs485.

Each slave should take different data. It is important that the data for the boards are sent at the same time.

My other solution is to create many master boards, but this solution is quite ineffective and expensive. (i.e. 50 slaves / 6 uarts ~= 9 master boards).

How I can extend uarts on my master board? I tried to use FTDI chip, but it allows to control only 4 more uarts.

I would be grateful for ideas. There are no bad answers here.

#microcontroller-projects #idea-needed #pcb-project #uart #ideas-needed

T J · ‎2018-05-31

Posted on June 01, 2018 at 02:09

You could write a bit blaster to run a whole port. // edit sorry for the infortuitous typo...

depending on the processor, you should be able to get 8 or 16 channels running.

a timer will control the bit rate.

3k x 50 is 150,000kbuad = 48M/150k = 320 cycles per bit ... uuumm only just, it will be difficult.

to manage 16 channels

I suggest that you use at least a 80MHz chip, to give 533 cycles per bit.

edit:

that give you about 1000 cycles at the end of each byte to source the next bytes,

AvaTar · ‎2018-06-04

Posted on June 04, 2018 at 10:23

Not sure if I understand.

But in difference to RS232, you can have multiple RS485 devices on one bus, not just two.

Use a protocol with addressing, and you can have all devices on one bus, with one UART.

Modbus or DMX512 come to my mind as examples.

The baud rates might get quite high in your case, or you could realize more (say, two or three) bus segments, controlled by different UARTs of the same master device

What do you intend to control ?

DMX512 is a throughput-oriented protocol of the 'fire-and-forget' variant, perhaps it suits your purpose.