What is uLan
uLan provides 9-bit message oriented communication protocol, which is transferred over RS-485 link. Characters are transferred same way as for RS-232 asynchronous transfer except parity bit, which is used to distinguish between data characters and protocol control information. A physical layer consists of one twisted pair of leads and RS-485 transceivers.
Use of 9-bit character simplifies transfer of binary data and for intelligent controllers can lower the CPU load, because of the CPU need not to care about data characters send to other node. Producers of most microcontrollers for embedded applications know that and have implemented 9-bit extension in UARTs of most of today's MCUs. There is the list below to mention some of them:
- many ARM based MCUs and SOCs ( NXP LPC 17xx, 4xxx, ... )
- members of Motorola 683xx family ( 68332, 68376, ... )
- Hitachi H8 microcontrollers
- all Intel 8051 and 8096 based MCUs with UART
Intel has developed a multiprotocol UART i82510, which is very well suited for implementing 9-bit communication interface for PC computers. The second example of the chip, which is well suited for 9-bit communication, is OX16C954-PCI produced by Oxford Semiconductors.
One of the problems of 9-bit communications is missing standardization of message protocol. Drivers and formats of one possible implementation of uLan message protocol are described below.