Part 1
What is the standard timing method for bits acquisition for a receiver using Modbus RTU?
For example, for UART: "Communicating UARTs have no shared timing system apart from the communication signal. Typically, UARTs resynchronize their internal clocks on each change of the data line that is not considered a spurious pulse. [...] they resynchronize on the falling edge of the start bit only, and then read the center of each expected data bit, and this system works if the broadcast data rate is accurate enough to allow the stop bits to be sampled reliably." (source wikipeda)
I didn't see that kind of information onto the modbus organization.org website.
Part 2
To go further, here is the issue:I use a FTDI F232R TTL USB cable (from RS-component) to make a custom sensor (server with a STM32 uC) communicate (using modbus protocole) with a computer (client), using a terminal (realterm) or a software (ModbusReader or custom) on it. I know I shouldn't do this because I have read that modbus protocole should be used with RS232 or RS485 physical layers, not TTL levels.. (I didn't find yet any explanation about that (?))Everything works fine at several baud rate speeds (i.e 115200, 19200, 1200) but at 57600 baud rate, it raises error (frame error on Modbus Reader).So, to know if there is any transmission issue (such as timing ones) on the line, I want to decode my self (using Scilab) the data recorded by an oscilloscope.
Note: strange thing: with an FTDI F232R TTL USB cable from an other (mysterious) source, which I opened to see that it uses same IC, but only 2 capacitors versus 4 capacitors on the RS-component source, I works pretty fine for all baud rate speed.
