how and what is best communication protocol between multiple micro-controller to one micro-controller(multiple slave to one master)

[RShar.9]

in that communication i have length issue (2 meter communication) , communication should be fast, less wire

[S.Ma]

Use RS485 transceivers. With STR495 ideal limit to be 20 Mbps.

In short range, SPI is the best solution (there is a way with a single NSS to address multiple slaves) at 12 Mbps (no transceivers) with up to 12 cascaded slaves

[RShar.9]

Thank you for your reply

SPI can be use up to 1 meter?

what is STR495?

Actually i m using 24 (not mistake it's 24) STM32 micro-controller and i m storing 5 ADC's value in SD-card (24 MCU has own individual SD-card) ,After task completed ( 3 days data will store in every SD-card, this ADC conversion process till 3 days (3000 SAMPLE PER SECOND)), i want to fetch all data from every SD-card and store in one SSD.

Please tell me the best way to complete this task.

[S.Ma]

3ksps x 16 bit = 6 kbyte/sec x 5 channels = 30 kbyte/sec x 3600 = 8 Gbyte storage per MCU

Then you will have to dump each MCU to a concentrator one and store 8 x 24 = 168 Gbyte of data in a microSD card...

Is your challenge to have 24 sensor pods far from each other, or you need lots of sensor in a very short range?

[RShar.9]

I have 24 sensor pods far from each other + data need to be dumped into one SSD(Solid state drive) from every SD-card(customer requirement)

[S.Ma]

In this case, you probably better off with USB HS or Ethernet connectivity to dump the microSD card content rather than use SPI or short range link.

You have to dump 8 gbyte (3 days log) into the SSD, so you need a high speed serial link.

[RShar.9]

What will be the speed of MCU'S USB protocol?

In USB or Ethernet connectivity can we use common port(single master and 24 slaves) to communicate to all 24 MCU's. is that possible?

actually once fixed we can not plug or unplug the communication connection. After system packed we can only communicate with SSD. Communication MCU'S to SSD should have less wire .

can single CPU Ethernet port communicate to all MCU's Ethernet port?

[S.Ma]

For example STM32F723 has USB HS (raw 400mbps), each device can be seen as mass storage and/or virtual com port for live feed.

USB Hubs cascaded as tree topology should be able to cater 24 devices. In 1999, old USB plug test "grand mele" was already achieving 32 devices...

Ethernet through routers is a well mature topology in severs to cater more than 24 devices.

If there is connectivity, you can live feed data like a webcam and follow the same topology and debug experience.

[S.Ma]

The main challenge with USB and Ethernet vs SPI or RS485 is that the STM32 will run middleware, and mastery of the stack will be required.

[Tesla DeLorean]

There might be a way to create a star-topology by suitably gating the signals. Perhaps via a simple CPLD or FPGA

The most robust might be to just use standard RJ45 connectors as use a couple of 16 port switches to connect up the nodes.

There might also be switch chips you could integrate onto your own board, but that would obviously make it a lot larger.