RS485 vs LIN

[vijay s]

hello friends
what is the difference between RS485 and LIN..both using UART and the function also looks similliar... can anybody clear this doubt
_________________
with regards
vijay s

[Ttelmah]

'RS485', is a _signalling standard only_. In itself, it defines nothing about 'what' is sent, just the voltages and drives used to send/receive the data. This is like RS232, which is also just a signalling standard, but is cmonly 'misused' to refer to simple async comms. Hence the CCS code, has a '#USE RS232' instruction, yet the PICs can't actually generate 'RS232'...
Yu can then have different 'protocols', _using_ RS485 signalling. So (for example), Profibus.
RS485, uses differential signalling, and is quite a robust signalling standard. Easily handling links over many hundreds of feet.
Depending on the protocols chosen, RS485, can support multi-master operation. By 'default', most links using RS485, use simple async operation, but with two more wires, you can of course use RS485, for fully sync data transmission.
LIN bus, is a complete 'bus specification', including both signalling standards, _and_ the data fomats involved. LIN, uses 12v signalling, but only single wire. The former 'improves' the reliability in noisy environments, while the latter is less good in this regard. Reception, is done on the assumption that the slave will synchronise itself to the transferred data, potentially removing the need for a crystal at the slave device. It is harder to generate LIN, using the standard UART. The actual data sent,is 'easy', but you need to add a 13bit 'sync' header in front of the transmitted data to provide the clock information. Reception is also harder, since again the PIC can receive the main data, but the 13bit header really needs external hardware, and to work properly a PLL, to synchronise the PICs clock to this frequency. However if only talking to 'off the shelf' slave devices, this doesn't have to be handled by the PIC, and the transmission end can be done by a simple delay loop.
LIN, is a 'synchronised' bus, as opposed to a 'synchronous' bus. Timing is sent once at the start of each communication.

Best Wishes

[vijay s]

hey
What is diagnostic message in LIN ? Is NAD mandatory for unconditional frame or the master can request any slaves with PID ?
reply please
_________________
with regards
vijay s