Laser PWM (K) - This is a three pin Molex Tripeg connector with ground, 1 input and 1 output. 5Vdc and ground, use the two screw terminals at the top right corner of the card. Two 5-pin headers are provided for use with RS485. The C/MRI is set up for full-duplex operation - two wires for transmitting from the PC and two wires for reception by the PC. In a serial interface the receiving and transmitting devices must operate at the same baud rate. This was developed in 1962 when the need for forms of transmitting data from modems attached telephone lines to remote communications equipments became apparent. DIP containing a Micro-Processor Unit (MPU), 8K 14-bit words of FLASH Program Memory, 368 bytes of RAM Data Memory, 256 bytes of EEPROM data memory, a Serial Communications Interface (SCI), built-in baud generator, three programmable timers, and an abundance of I/O pins. The heart of the SMINI is part U1, a Microchip Technology PIC16F877-20/P Microcontroller with built-in FLASH memory, making it a smart interface. A big advantage of the 877’s FLASH memory is that the ultraviolet erase cycle is not required as it was for the MC68701, used with the previous USIC.

Programming the PIC16F877 FLASH memory requires a special PIC Micro Programmer package. PIC processors are the most popular family of microcontrollers and the 877 is ideally suited for our interfacing needs. Because typical computer interfacing distances are very short compared to the 4000-foot limit of RS485, the type of cable used is not overly important. Proper cable termination, a topic covered near the end of this chapter becomes increasingly important as cable length is increased. Only one end of the bus requires the resistor network. I find it easiest to think of the SMINI card as being four cards combined into one, an SUSIC combined with two 24-bit output cards and one 24-bit input card. I will refer to these "cards within a card" as "Cards 0 and 1" for providing the 48-outputs and as "Card 2" for providing the 24-inputs. You will find these nomenclatures used along the left, bottom and right edges of the SMINI card.

Selecting an interface standard that is no longer active and supported may make it hard to find both component and support. It is also possible to convert between RS485 and RS232 using simple interface converters that may include optical isolation between the two circuits as well as surge suppression for any electrical 'spikes' that may be picked up. The use of the terms bit and byte will become second nature as you begin to put the interface to use. In "computer-ese" we refer to each pin, or line, as a bit and 8 bits become a byte. The SMINI and the SUSIC are designed to operate with standard baud rates of 9600, 19200, 28800, 57600 and 115200 bits per second or bps. This is significant because a serial interface transmits data sequentially, one bit after another, as opposed to a parallel interface, which for example might transmit one byte (eight bits) at a time.

Thus each port handles 8 bits, or 1 byte of data, either input or output. This is accomplished by using RC5, Pin 24, as a transmit enable line connected to U7’s driver enable (DE) input. It is a very rugged static protected design with built-in TTL compatibility including high sink/source current capability of 25mA per I/O line. 5 meters away on the high contrast display. Also, for applications where you desire to filter out high frequency noise, it is better to use tantalum, disk ceramic or monolithic capacitors in place of the frequently lower-priced electrolytic capacitors, which are less effective at the higher frequencies. And, because we are using the more advanced RS485 ICs, we expand our maximum node capability from 16 to 128. Because of this doubling up of the number of RS485 transceiver ICs and the corresponding use of 4-wires, this arrangement is typically referred to throughout the commercial and industrial world as a "Full Duplex" implementation of RS485.

In the event you loved this information and you would love to receive details regarding RS485 standard assure visit our webpage.