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| 型號： | RFEVAL1-SYS |
| 英文描述： | EVALUATION BOARD RF |
| 中文描述： | 評價委員會射頻 |
| 文件頁數(shù)： | 7/19頁 |
| 文件大?。?/td> | 614K |
| 代理商： | RFEVAL1-SYS |
DS000023 Ver 1.1 JAN 00
1999 Reg. No. 227 4001, ENGLAND
Page 7
R
ADIO
E
VALUATION
K
IT
RFEVAL1
PROJECT #3;
TRANSMITTING A DATA BYTE BETWEEN TWO PC'S
Encoder Schematic : Fig 72
Decoder Schematic : Fig 74
This project looks briefly at the problems of passing serial data over a low power radio link and takes the
designer down the first steps in designing a simple ‘Radio Packet Controller’ (RPC) which could be extended
to include error detection and other more advanced features.
It is not possible to simply feed asynchronous data into a radio module and expect the data to emerge
'unscathed' from the receiver module. For this reason a ‘Radio Packet Controller’ (RPC) is available
specifically designed to enable asynchronous data transmission
The basic problem with transmitting serial asynchronous data between say a couple of PC's is that the data
content is not likely to be ‘balanced’ (100% ac content). This would cause the radio module receiver to
malfunction because of the receive data slice circuitry becoming biased by a cumulative string of '1' or '0' bits
which appear in the received data. It may in some instances be possible to encode the data in the transmitting
PC such that this problem is minimised, but in general this is not a valid option. Most applications will require
an interface between the RS232 port on the PC and the radio transmitter module, which codes the data to give
optimum performance from the radio link irrespective of the content of the data which is being transmitted.
This function is normally combined with the creation of a data packet structure where individual characters are
not transmitted, but instead a number is sent at a point in time in a composite frame. This also provides
receiver biasing and error detection.
The principle of the RPC which is described in this project is simple, the RS232 serial port on the transmitter is
used to receive characters from a PC. When eight characters have been received, they are formed into a
packet and transmitted as a frame. The frame has a header, and a sync byte, and the data characters are
coded in Manchester format. This is similar to the format utilised in the Microchip HCS360 encoder.
The receiving software decodes the frame and outputs the characters on an RS232 port. The system has
been designed to be a demonstration of the principles of an RPC and requires that the user enter characters in
blocks of 8 with a pause between each block. This is clearly a limitation on the user, which in practice might
not be acceptable. However by using the software for this project as a starting point, the software engineer
should be able to overcome this by implementing interrupt driven communications and more complex buffering
at both ends of the link.
The transmitter and receiver boards both use the PIC16C73A processor and these devices communicate with
the PC's using the PIC on board UART's and over RS232 data links which are supported by the on board level
shifter circuitry. The system will function with either AM or FM radio modules and is an excellent way of
carrying out module selection and also as a means of testing out different aerial systems.
The software for the transmitter runs in a PIC16C73A and consists of two main blocks which carry out the
following functions:
1. Transmitter reception of 8 data bytes and their transfer into a buffer from the host PC using the
PIC16C73’s on board UART.
2. Transmission of a frame of RF data consisting of a preamble, a synchronous element, the actual
data block itself in Manchester format and a guard period.
The software for the receiver runs in a PIC 16C73 and again consists of two main blocks which carry out the
following functions:
1. Reception of the frame and transfer of the data into a buffer.
2. Transmission of the 8 data bytes to the PC using the on board UART.
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