Modbus Test Software is a sniffer tool that allows you to analyze RS232/RS422/RS485 interfaces transmitting MODBUS communications. SPM’s excellent functionality enables easy detection and resolution of problems encountered when engaged in MODBUS testing and debugging. Abstract: Three common serial data standards, RS-232, RS-422, and RS-485, are described by specification and electrical interface. Cable termination techniques, use of multiple loads, daisy-chaining of RS-232, conversion of RS-232 to RS-485, conversion of RS-485 to RS-232, and RS-232 port-powered RS-485 conversions are described.

A UART is a Universal Asynchronous Receiver/Transmitter that converts parallel data from the host processor (any Mosaic controller) into a serial data stream. Each of the two UARTs on the wildcard is capable of full-duplex communications, meaning that both transmission and reception can occur simultaneously (although the RS485 protocol is half duplex as explained below). In other words, each local UART on the wildcard can both send data to and receive data from a remote UART on the other end of a connecting serial cable. The local and remote must share a common ground, so all serial cables include at least one ground conductor. The words port and channel are used interchangeably to refer to a serial communications link. The UART Wildcard provides two simultaneous communications links, each configurable as RS232, RS485 or RS422.

The serial interface is asynchronous, meaning that there is no clock transmitted along with the data. Rather, the transmitter and receiver must be communicating using a known baud rate, or bit frequency. Both the local and remote UARTs must be configured for the same baud rate.

Software-selectable baud rates up to 56,000 baud are supported. You can use the driver function Set_Baud to specify the baud rate. The actual baud rate produced differs from that requested by a small error owing to rounding of an internal divisor. The baud rate produced is. Where Baud desired is an unsigned integer from 1 to 56000, 500000 is the frequency of the UART's internal clock and Round(500000/Baud desired) is an internal divisor (rounded to the nearest integer).

Mix all ingredients in a bowl and then spread into a pie plate. Then, top with 8 slices of crumbled bacon.

So long as the error between the actual baud rate and that specified is less than 1.5% (or the error between transmitter and receiver is less than 3%) there should be no communication errors. Baud rates up to 56,000 baud are supported. 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. Modem to modem lines often use 1200, 4800, 9600, 14400, 28800, 33600, and 56000 baud.

Port to modem communications usually use 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 baud. Of these baud rates in common use, the UART Wildcard can produce the following at high accuracy.

Programming Common Baud Rates Specified Baud Divisor Actual Baud Error (%) 110 4545 110 0.01 150 3333 150 0.01 300 1667 300 -0.02 600 833 600 0.04 1200 417 1199 -0.08 2400 208 2404 0.16 3000 167 2994 -0.20 3200 156 3205 0.16 4800 104 4808 0.16 96 0.16 1446 -0.79 1921 0.16 3363 -0.79 3842 0.16 56000 9 55556 -0.79 Both the local and remote UARTs must be configured for the same baud rate. You may use nonstandard baud rates if both devices support them. The UART Wildcard supports any baud rate produced by the above formula. Serial data is shifted out least-significant-bit first. At the UART, a logic high (5 volts) is called a mark, and a logic low (0 volts) is called a space. The serial output at the UART idles at the logic high (mark) level.

A logic-low start bit marks the start of a character, followed by 5 to 8 data bits per character. An optional parity bit can be specified to enable error detection by the UART.

One to two logic-high stop bits mark the end of a character. Parity options include even, odd, high, low, or no parity. Even parity means that the bits sum to an even number, and odd parity means that the bits sum to an odd number. High (mark) parity means that the parity bit is always logic 1 at the UART, and low (space) parity means that the parity bit is always logic 0 at the UART. No parity means that there is no parity bit. A break sequence forces the serial output to a logic low (space) at the UART.