A
My project is design and implementation of an industrial automation communication link between a master (a pc) and 40 slaves (8051 microcontroller boards), (via 20 rs485 ports of master). We chose STAR topology and the link baud rate must be 2MBps (Asynchronous). we must include CRC checking. our frame length must be restricted to 10 bytes (we have 4 data bytes).
at the first stage i chose MODBUS protocol for doing that, but i found out that its baud rate is restricted to 1MBps, although the medium used is RS485 & as you know better, its baud may be a value up to 2MBps, i don't know which parameters of MODBUS restrict baud rate, and if we can choose a higher baud rate of 2mBps.
beside this, as we know MODBUS is an application layer protocol and it utilizes HDLC as it's layer 2 protocol. so i'm confused that by considering this, how MODBUS (an asynchronous protocol) is joint to HDLC (a synchronous one) and i don't know if i can use only one of these two for my project or not.
at last, i don't know how to program the link between layer 7 (MODBUS) and layer 2 (HDLC) if i have to do so. finally i do thank you alot in advance for your help and i'll be so grateful if you send me some source code that will help me.
at the first stage i chose MODBUS protocol for doing that, but i found out that its baud rate is restricted to 1MBps, although the medium used is RS485 & as you know better, its baud may be a value up to 2MBps, i don't know which parameters of MODBUS restrict baud rate, and if we can choose a higher baud rate of 2mBps.
beside this, as we know MODBUS is an application layer protocol and it utilizes HDLC as it's layer 2 protocol. so i'm confused that by considering this, how MODBUS (an asynchronous protocol) is joint to HDLC (a synchronous one) and i don't know if i can use only one of these two for my project or not.
at last, i don't know how to program the link between layer 7 (MODBUS) and layer 2 (HDLC) if i have to do so. finally i do thank you alot in advance for your help and i'll be so grateful if you send me some source code that will help me.