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We’ll use code from the GETSTART.c program which was introduced in the chapter titled Your First Program. In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port - and you didn’t even have to recompile the code! If you are using the QScreen as a slave device and require the /SS signal for your external SPI hardware, configure one of the Port A pins on the Field Header as an input pin. The master and slave could even exchange ascii QED-Forth commands. The master and slave could even exchange ascii QED-Forth operating system commands. The byte-sized messages are transmitted and received via the MOSI (master out/slave in) and MISO (master in/slave out) pins. The two jacks are for RS485 cable in and RS485 cable out. You aren’t limited to fifty feet of cable like with RS232. So what is a RS232 to RS485 converter? So that's how converter rs485 being used.

This section describes the driver routines that control the RS485 transceiver, and presents some ideas that may prove useful in designing a multi-drop data exchange protocol. The SPIE bit in the SPCR (SPI control register) enables SPI interrupt handling. Hardware is interfaced to the SPI via three PORTD pins named SCK, MOSI, and MISO brought out to pins 7, 8, and 10 on the Wildcard Port Header (see Appendix B). Serial data is shifted out least-significant-bit first. A FIFO is a First In/First Out buffer that can queue a burst of outgoing characters for transmission, or save a set of incoming characters until the host can read them. The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii "name" of this particular slave). The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii name of this particular slave). The above parity settings will also determine how incoming data is interpreted (whether the most significant bit is considered a parity bit or part of the data being transmitted, and how many bits total to expect in each byte).

So, for eight data bits with a parity bit, M would be set (equal to one) in order to add an extra bit to each byte transmitted, and PE would be set in order to make that extra bit be used as a parity bit. This is an extra single bit appended to the end of each byte or character transmitted, which is set or cleared as necessary to ensure that the total number of '1' bits in the byte is always odd or even. To ensure that no two devices drive the network at the same time, it is necessary that each slave device be able to disable its own RS485 data transmitter. The flexibility and power of the 68HC11’s serial peripheral interface supports high speed communication between the 68HC11 and other synchronous serial devices. With careful design, many peripherals can communicate via the SPI, and powerful multi-processor systems can be linked using this high speed bus. The serial output at the UART idles at the logic high (mark) level. A break sequence forces the serial output to a logic low (space) at the UART. An optional parity bit can be specified to enable error detection by the UART.

Parity options include even, odd, high, low, or no parity. If two bits are received incorrectly, the error will go unnoticed by parity checking. The UART Wildcard provides two simultaneous communications links, each configurable as RS232, RS485 or RS422. Two auxiliary power cables should always be connected for digital instruments. These cables allow the dual RJ11 jacks of the RS485 option board of Laureate meters (digital interface ordering option 2) to be daisy chained and to be addressed digitally with no need for a hub. Laureate RS485 boards are available in versions with dual RJ11 jacks (ordering option 2, board P/N L485) and with dual RJ485 jacks (ordering option 4, board P/N LMOD). Should I use RJ11 or RJ45 connectors? The RJ11 socket is interesting, because the manufacturer choose to have a symmetrical pin-layout, just as with the MMJ connector on DECconnect systems and the RJ45 jack in the Yost standard. We assume that you are now communicating with the PDQ Board via the default Serial1 port at the standard 115200 baud rate. There are different sets of standard baud rates in use depending on the application. Modem to phone line communications use rates of 110, 150, 300, 600, 1200, 2400, 3000, and 3200 baud.